Add Buddypress xProfile Languages select field

bp-custom.php

<?php
/*
Add a Language (multi) select field to Buddypress xProfile fields.
You can adapt it to any other type of select field, for example one with list of Countries, Cities, etc...
Add the following to /wp-content/plugins/bp-custom.php and then visit /wp-admin/users.php?page=bp-profile-setup

Read more about bp-custom.php at the official Buddypress https://codex.buddypress.org/themes/bp-custom-php/
*/

function bp_add_languages_xprofile_select_field() {
    if (!xprofile_get_field_id_from_name('Languages') && $_GET['page'] == 'bp-profile-setup') {
        $languagesFieldId = xprofile_insert_field([
            'field_group_id' => 1,
            'name' => 'Languages',
            'description' => 'Please select your languages',
            'type' => 'multiselectbox', // change to "selectbox" if desired
            'is_required' => false,
            'order_by' => 'custom',
            'field_order' => 2,
            'can_delete' => true,
        ]);
        if ($languagesFieldId) {
            $languages = [
                'Afrikaans',
                'Albanian - shqip',
                'Amharic - አማርኛ',
                'Arabic - العربية',
                'Aragonese - aragonés',
                'Armenian - հայերեն',
                'Asturian - asturianu',
                'Azerbaijani - azərbaycan dili',
                'Basque - euskara',
                'Belarusian - беларуская',
                'Bengali - বাংলা',
                'Bosnian - bosanski',
                'Breton - brezhoneg',
                'Bulgarian - български',
                'Catalan - català',
                'Central Kurdish - کوردی (دەستنوسی عەرەبی)',
                'Chinese - 中文',
                'Chinese (Hong Kong) - 中文（香港）',
                'Chinese (Simplified) - 中文（简体）',
                'Chinese (Traditional) - 中文（繁體）',
                'Corsican',
                'Croatian - hrvatski',
                'Czech - čeština',
                'Danish - dansk',
                'Dutch - Nederlands',
                'English',
                'English (Australia)',
                'English (Canada)',
                'English (India)',
                'English (New Zealand)',
                'English (South Africa)',
                'English (United Kingdom)',
                'English (United States)',
                'Esperanto - esperanto',
                'Estonian - eesti',
                'Faroese - føroyskt',
                'Filipino',
                'Finnish - suomi',
                'French - français',
                'French (Canada) - français (Canada)',
                'French (France) - français (France)',
                'French (Switzerland) - français (Suisse)',
                'Galician - galego',
                'Georgian - ქართული',
                'German - Deutsch',
                'German (Austria) - Deutsch (Österreich)',
                'German (Germany) - Deutsch (Deutschland)',
                'German (Liechtenstein) - Deutsch (Liechtenstein)',
                'German (Switzerland) - Deutsch (Schweiz)',
                'Greek - Ελληνικά',
                'Guarani',
                'Gujarati - ગુજરાતી',
                'Hausa',
                'Hawaiian - ʻŌlelo Hawaiʻi',
                'Hebrew - עברית',
                'Hindi - हिन्दी',
                'Hungarian - magyar',
                'Icelandic - íslenska',
                'Indonesian - Indonesia',
                'Interlingua',
                'Irish - Gaeilge',
                'Italian - italiano',
                'Italian (Italy) - italiano (Italia)',
                'Italian (Switzerland) - italiano (Svizzera)',
                'Japanese - 日本語',
                'Kannada - ಕನ್ನಡ',
                'Kazakh - қазақ тілі',
                'Khmer - ខ្មែរ',
                'Korean - 한국어',
                'Kurdish - Kurdî',
                'Kyrgyz - кыргызча',
                'Lao - ລາວ',
                'Latin',
                'Latvian - latviešu',
                'Lingala - lingála',
                'Lithuanian - lietuvių',
                'Macedonian - македонски',
                'Malay - Bahasa Melayu',
                'Malayalam - മലയാളം',
                'Maltese - Malti',
                'Marathi - मराठी',
                'Mongolian - монгол',
                'Nepali - नेपाली',
                'Norwegian - norsk',
                'Norwegian Bokmål - norsk bokmål',
                'Norwegian Nynorsk - nynorsk',
                'Occitan',
                'Oriya - ଓଡ଼ିଆ',
                'Oromo - Oromoo',
                'Pashto - پښتو',
                'Persian - فارسی',
                'Polish - polski',
                'Portuguese - português',
                'Portuguese (Brazil) - português (Brasil)',
                'Portuguese (Portugal) - português (Portugal)',
                'Punjabi - ਪੰਜਾਬੀ',
                'Quechua',
                'Romanian - română',
                'Romanian (Moldova) - română (Moldova)',
                'Romansh - rumantsch',
                'Russian - русский',
                'Scottish Gaelic',
                'Serbian - српски',
                'Serbo-Croatian - Srpskohrvatski',
                'Shona - chiShona',
                'Sindhi',
                'Sinhala - සිංහල',
                'Slovak - slovenčina',
                'Slovenian - slovenščina',
                'Somali - Soomaali',
                'Southern Sotho',
                'Spanish - español',
                'Spanish (Argentina) - español (Argentina)',
                'Spanish (Latin America) - español (Latinoamérica)',
                'Spanish (Mexico) - español (México)',
                'Spanish (Spain) - español (España)',
                'Spanish (United States) - español (Estados Unidos)',
                'Sundanese',
                'Swahili - Kiswahili',
                'Swedish - svenska',
                'Tajik - тоҷикӣ',
                'Tamil - தமிழ்',
                'Tatar',
                'Telugu - తెలుగు',
                'Thai - ไทย',
                'Tigrinya - ትግርኛ',
                'Tongan - lea fakatonga',
                'Turkish - Türkçe',
                'Turkmen',
                'Twi',
                'Ukrainian - українська',
                'Urdu - اردو',
                'Uyghur',
                'Uzbek - o‘zbek',
                'Vietnamese - Tiếng Việt',
                'Walloon - wa',
                'Welsh - Cymraeg',
                'Western Frisian',
                'Xhosa',
                'Yiddish',
                'Yoruba - Èdè Yorùbá',
                'Zulu - isiZulu'
            ];

            $i = 1;
            foreach ( $languages as $language ) {
                xprofile_insert_field([
                    'field_group_id'	=> 1,
                    'parent_id' => $languagesFieldId,
                    'type' => 'option',
                    'name' => $language,
                    'option_order' => $i
                ]);
                $i++;
            }
        }
    }
}
add_action('bp_init', 'bp_add_languages_xprofile_select_field');