Modified version of Henk's 'Keep Native Lang Plus Eng' Tdarr plugin to keep only the original language track & user specified language tracks. Works with both Radarr & Sonarr.

Mod_Tdarr_Plugin_henk_Keep_Native_Lang_Plus_Other_Spec_Lang.txt

/* eslint-disable no-await-in-loop */
module.exports.dependencies = ['axios@0.27.2', '@cospired/i18n-iso-languages'];

const details = () => ({
  id: 'Tdarr_Plugin_henk_Keep_Native_Lang_Plus_Eng',
  Stage: 'Pre-processing',
  Name: 'Remove all langs except native and English',
  Type: 'Audio',
  Operation: 'Transcode',
  Description: `This is a modified version made by gsariev of the original plugin. This plugin will remove all language audio tracks except the 'native' and user-specified languages.
     (requires TMDB api key).
    'Native' languages are the ones that are listed on TMDB. It does an API call to 
    Radarr, Sonarr to check if the movie/series exists and grabs the IMDb id. As a last resort, it 
    falls back to the IMDb id in the filename.`,
  Version: '1.2',
  Tags: 'pre-processing,configurable',
  Inputs: [
    {
      name: 'user_langs',
      type: 'string',
      defaultValue: '',
      inputUI: {
        type: 'text',
      },
      tooltip:
        'Input a comma-separated list of ISO-639-2 languages. It will still keep English and undefined tracks.'
        + '(https://en.wikipedia.org/wiki/List_of_ISO_639-2_codes 639-2 column)'
        + '\\nExample:\\n'
        + 'ger,fre',
    },
    {
      name: 'priority',
      type: 'string',
      defaultValue: 'radarr',
      inputUI: {
        type: 'text',
      },
      tooltip:
        'Priority for either Radarr or Sonarr. Leaving it empty defaults to Radarr first.'
        + '\\nExample:\\n'
        + 'sonarr',
    },
    {
      name: 'api_key',
      type: 'string',
      defaultValue: '',
      inputUI: {
        type: 'text',
      },
      tooltip:
        'Input your TMDB api (v3) key here. (https://www.themoviedb.org/)',
    },
    {
      name: 'radarr_api_key',
      type: 'string',
      defaultValue: '',
      inputUI: {
        type: 'text',
      },
      tooltip: 'Input your Radarr api key here.',
    },
    {
      name: 'radarr_url',
      type: 'string',
      defaultValue: '192.168.1.2:7878',
      inputUI: {
        type: 'text',
      },
      tooltip:
        'Input your Radarr url here. (Without http://). Do include the port.'
        + '\\nExample:\\n'
        + '192.168.1.2:7878',
    },
    {
      name: 'sonarr_api_key',
      type: 'string',
      defaultValue: '',
      inputUI: {
        type: 'text',
      },
      tooltip: 'Input your Sonarr api key here.',
    },
    {
      name: 'sonarr_url',
      type: 'string',
      defaultValue: '192.168.1.2:8989',
      inputUI: {
        type: 'text',
      },
      tooltip:
        'Input your Sonarr url here. (Without http://). Do include the port.'
        + '\\nExample:\\n'
        + '192.168.1.2:8989',
    },
    {
      name: 'commentary',
      type: 'boolean',
      defaultValue: false,
      inputUI: {
        type: 'dropdown',
        options: [
          'false',
          'true',
        ],
      },
      tooltip: `Specify if audio tracks that contain commentary/description should be removed.
               \\nExample:\\n
               true

               \\nExample:\\n
               false`,
    },
  ],
});

const response = {
  processFile: false,
  preset: ', -map 0 ',
  container: '.',
  handBrakeMode: false,
  FFmpegMode: true,
  reQueueAfter: false,
  infoLog: '',
};

const languageConverter = (tmdbLanguageCode) => {
  const isoLang = require('@cospired/i18n-iso-languages');

  try {
    // Convert TMDB language code to ISO-639-2 3-letter format
    const convertedLanguageCode = isoLang.alpha2ToAlpha3B(tmdbLanguageCode);

    // Log the converted language code
    response.infoLog += `TMDB Language Code Return: ${convertedLanguageCode}\n`;

    return convertedLanguageCode;
  } catch (error) {
    console.error('Error converting language code:', error.message);
    response.infoLog += '☒Error converting language code.\n';
    return null;
  }
};

const parseArrResponse = (body, filePath, arr) => {
  // eslint-disable-next-line default-case
  switch (arr) {
    case 'radarr':
      return body.movie;
    case 'sonarr':
      return body.series;
  }
};

const processStreams = (result, file, userLangs, isSonarr, includeCommentary) => {
  const languages = require('@cospired/i18n-iso-languages');
  const tracks = {
    keep: [],
    remove: [],
    remLangs: '',
  };
  let streamIndex = 0;

  // Convert the TMDB language code to ISO-639-2 3-letter format dynamically
  const tmdbLanguageCode = result.original_language;
  const convertedLanguageCode = languageConverter(tmdbLanguageCode) || tmdbLanguageCode;

  response.infoLog += `Original language tag: ${convertedLanguageCode}\n`;

  // Add the original language to the list of languages to keep
  tracks.keep.push(streamIndex);
  response.infoLog += `Keeping the original language audio track: ${languages.getName(result.original_language, 'en')}\n`;

  // Flag to indicate if any audio track matches the specified languages
  let matchFound = false;

  for (const stream of file.ffProbeData.streams) {
    if (stream.codec_type === 'audio') {
      if (!stream.tags) {
        response.infoLog += `☒No tags found on audio track ${streamIndex}. Removing it.\n`;
        tracks.remove.push(streamIndex);
        response.preset += `-map -0:a:${streamIndex} `;
      } else if (stream.tags.title && isCommentaryTrack(stream.tags.title)) {
        // Remove commentary tracks if includeCommentary is true
        if (includeCommentary) {
          response.infoLog += `☒Removing commentary audio track: ${languages.getName(stream.tags.language, 'en')} (commentary) - ${stream.tags.title}\n`;
          tracks.remove.push(streamIndex);
          response.preset += `-map -0:a:${streamIndex} `;
          tracks.remLangs += `${languages.getName(stream.tags.language, 'en')} (commentary), `;
        }
      } else if (stream.tags.language) {
        // Check if the language is in the user-defined languages or it's the original language
        const mappedLanguage = isSonarr ? mapSonarrLanguageToTMDB(stream.tags.language) : mapRadarrLanguageToTMDB(stream.tags.language);
        
        if (userLangs.includes(mappedLanguage) || mappedLanguage === convertedLanguageCode) {
          tracks.keep.push(streamIndex);
          response.infoLog += `☑Keeping audio track with language: ${languages.getName(stream.tags.language, 'en')}\n`;
          matchFound = true; // At least one track matches the specified languages
        } else {
          response.infoLog += `☒Removing audio track with language: ${languages.getName(stream.tags.language, 'en')}\n`;
          tracks.remove.push(streamIndex);
          response.preset += `-map -0:a:${streamIndex} `;
          tracks.remLangs += `${languages.getName(stream.tags.language, 'en')}, `;
        }
      } else {
        response.infoLog += `☒No language tag found on audio track ${streamIndex}. Removing it.\n`;
        tracks.remove.push(streamIndex);
        response.preset += `-map -0:a:${streamIndex} `;
      }

      streamIndex += 1;
    }
  }

  response.preset += ' -c copy -max_muxing_queue_size 9999';

  // If none of the audio tracks match the specified languages, stop the plugin
  if (!matchFound) {
    response.infoLog += '☒Cancelling plugin because none of the audio tracks match the specified languages. \n';
    response.processFile = false;

    // Clear the removal tracks to prevent further deletion
    tracks.remove = [];
  }

  return tracks;
};

const mapRadarrLanguageToTMDB = (radarrLanguage) => {
  const languageMappings = {
    chi: 'cn',
    // Add additional mapping if needed
  };

  return languageMappings[radarrLanguage] || radarrLanguage;
};

const mapSonarrLanguageToTMDB = (sonarrLanguage) => {
  const languageMappings = {
    // Add mappings for Sonarr languages if needed
  };

  return languageMappings[sonarrLanguage] || sonarrLanguage;
};

const tmdbApi = async (filename, api_key, axios) => {
  let fileName;

  if (filename) {
    if (filename.slice(0, 2) === 'tt') {
      fileName = filename;
    } else {
      const idRegex = /(tt\d{7,8})/;
      const fileMatch = filename.match(idRegex);

      if (fileMatch) {
        fileName = fileMatch[1];
      }
    }
  }

  if (fileName) {
    try {
      const result = await axios
        .get(
          `https://api.themoviedb.org/3/find/${fileName}?api_key=`
          + `${api_key}&language=en-US&external_source=imdb_id`,
        )
        .then((resp) => (resp.data.movie_results.length > 0
          ? resp.data.movie_results[0]
          : resp.data.tv_results[0]));

      console.log('TMDB API Result:', result);

      if (!result) {
        response.infoLog += '☒No IMDb result was found. \n';
      }

      if (result) {
        const tmdbLanguageCode = languageConverter(result.original_language);

        response.infoLog += `Converted TMDB Language Code: ${tmdbLanguageCode}\n`;
        response.infoLog += `Language tag picked up by TMDB: ${tmdbLanguageCode}\n`;
      } else {
        response.infoLog += "☒Couldn't find the IMDb id of this file. Skipping. \n";
      }

      return result;
    } catch (error) {
      console.error('Error fetching data from TMDB API:', error.message);
      response.infoLog += '☒Error fetching data from TMDB API.\n';
      return null;
    }
  }

  return null;
};

const isCommentaryTrack = (title) => {
  // Check if the title includes keywords indicating a commentary track
  return title.toLowerCase().includes('commentary')
    || title.toLowerCase().includes('description')
    || title.toLowerCase().includes('sdh');
};

const plugin = async (file, librarySettings, inputs, otherArguments) => {
  const lib = require('../methods/lib')();
  const axios = require('axios').default;

  inputs = lib.loadDefaultValues(inputs, details);

  response.container = `.${file.container}`;
  let prio = ['radarr', 'sonarr'];
  let radarrResult = null;
  let sonarrResult = null;
  let tmdbResult = null;

  if (inputs.priority && inputs.priority === 'sonarr') {
    prio = ['sonarr', 'radarr'];
  }

  const fileNameEncoded = encodeURIComponent(file.meta.FileName);

  for (const arr of prio) {
    let imdbId;

    // Reset infoLog before each processing step (removes duplicated logs being displayed)
    response.infoLog = '';

    switch (arr) {
      case 'radarr':
        if (tmdbResult) break;
        if (inputs.radarr_api_key) {
          radarrResult = parseArrResponse(
            await axios
              .get(
                `http://${inputs.radarr_url}/api/v3/parse?apikey=${inputs.radarr_api_key}&title=${fileNameEncoded}`,
              )
              .then((resp) => resp.data),
            fileNameEncoded,
            'radarr',
          );

          if (radarrResult) {
            imdbId = radarrResult.imdbId;
            response.infoLog += `Grabbed ID (${imdbId}) from Radarr \n`;

            const radarrLanguageTag = radarrResult.originalLanguage.name;
            response.infoLog += `Language tag picked up by Radarr: ${radarrLanguageTag}\n`;

            tmdbResult = await tmdbApi(imdbId, inputs.api_key, axios);

            if (tmdbResult) {
              const tmdbLanguageTag = languageConverter(tmdbResult.original_language) || tmdbResult.original_language;
              response.infoLog += `Language tag picked up by TMDB: ${tmdbLanguageTag}\n`;
            }
          } else {
            response.infoLog += "Couldn't grab ID from Radarr \n";
            imdbId = fileNameEncoded;
            tmdbResult = await tmdbApi(imdbId, inputs.api_key, axios);

            if (tmdbResult) {
              const tmdbLanguageTag = languageConverter(tmdbResult.original_language) || tmdbResult.original_language;
              response.infoLog += `Language tag picked up by TMDB: ${tmdbLanguageTag}\n`;
            }
          }
        }
        break;
      case 'sonarr':
        if (tmdbResult) break;
        if (inputs.sonarr_api_key) {
          sonarrResult = parseArrResponse(
            await axios.get(
              `http://${inputs.sonarr_url}/api/v3/parse?apikey=${inputs.sonarr_api_key}&title=${fileNameEncoded}`,
            )
              .then((resp) => resp.data),
            file.meta.Directory,
            'sonarr',
          );

          if (sonarrResult) {
            imdbId = sonarrResult.imdbId;
            response.infoLog += `Grabbed ID (${imdbId}) from Sonarr \n`;

            tmdbResult = await tmdbApi(imdbId, inputs.api_key, axios);

            if (tmdbResult) {
              const sonarrTracks = processStreams(tmdbResult, file, inputs.user_langs ? inputs.user_langs.split(',') : '', true, inputs.commentary);

              if (sonarrTracks.remove.length > 0) {
                if (sonarrTracks.keep.length > 0) {
                  response.infoLog += `☑Removing tracks with languages: ${sonarrTracks.remLangs.slice(
                     0,
                     -2,
                  )}. \n`;
                  response.processFile = true;
                  response.infoLog += '\n';
                } else {
                  response.infoLog
                    += '☒Cancelling plugin otherwise all audio tracks would be removed. \n';
                }
              } else {
                response.infoLog += '☒No audio tracks to be removed. \n';
              }
            } else {
              response.infoLog += "☒Couldn't find the IMDb id of this file. Skipping. \n";
            }
          }
        }
        break;
    }
  }

  if (tmdbResult) {
    const userLanguages = inputs.user_langs ? inputs.user_langs.split(',') : [];
    const originalLanguage = tmdbResult.original_language;
    const originalLanguageIncluded = userLanguages.includes(originalLanguage);

    const tracks = processStreams(
      tmdbResult,
      file,
      userLanguages,
      false,
      inputs.commentary,
    );

    console.log('Tracks:', tracks);
    console.log('Original Language:', originalLanguage);
    console.log('User Languages:', userLanguages);
    console.log('Original Language Included:', originalLanguageIncluded);
    console.log('User Languages Include Removed Languages:', userLanguages.includes(tracks.remLangs));

    // Check if no tracks match original or user-specified languages
    const noMatchingTracks = tracks.keep.length === 0 && !originalLanguageIncluded && !userLanguages.includes(tracks.remLangs);

    console.log('No Matching Tracks:', noMatchingTracks);

    if (noMatchingTracks) {
      response.infoLog += '☒Cancelling plugin because no audio tracks match the original language or user-specified languages. \n';
      return response; // Stop execution
    }

    // Continue processing audio tracks
    if (tracks.remove.length > 0) {
      if (tracks.keep.length > 0) {
        response.infoLog += `☑Removing tracks with languages: ${tracks.remLangs.slice(
          0,
          -2,
        )}. \n`;
        response.processFile = true;
        response.infoLog += '\n';
      } else {
        response.infoLog += '☒Cancelling plugin otherwise all audio tracks would be removed. \n';
      }
    } else {
      response.infoLog += '☒No audio tracks to be removed. \n';
    }
  } else {
    response.infoLog += "☒Couldn't find the IMDb id of this file. Skipping. \n";
  }

  return response;
};

module.exports.details = details;
module.exports.plugin = plugin;

Thought I'd follow up. The change I made, replacing the condition in the Sonarr case with the Radarr one, ended up running with no error and produced the following command:

Args: -i "/mnt/data/tv.mkv" -map 0 -map -0:a:2 -c copy -max_muxing_queue_size 9999 "/temp/tv-TdarrCacheFile-mplgky3ut.mkv"

If I were to guess your suggested change of setting the preset to an empty string, '', would work as well but you would still end up running processStreams() twice which may be inefficient unless the processing in the Sonarr case is necessary.

EDIT:
I did find the plugin from the guide you made in the Tdarr subreddit. Thanks again for that post.