The script to translate sentences by using the web api created with Google Apps Script.

setting.json

{
    "url": "https://url.to.your.webapp",
    "source": "en",
    "target": "ja",
    "langs": [
        "en",
        "ja",
        "zh-cn",
        "de"
    ]
}

translation2.py

import ui
import appex
import dialogs
import console
from objc_util import *

import json
import urllib3
from urllib3.exceptions import InsecureRequestWarning

urllib3.disable_warnings(InsecureRequestWarning)

setting = None
http = None
v = None

def main():
    global setting, http, v
    setting = get_setting()
    http = urllib3.PoolManager()

    text = appex.get_text()
    v = ui.load_view()
    ui_initialize(text)
    v.present('sheet')

def translate(text):
    query = {
        'text': text,
        'source': setting['source'],
        'target': setting['target'],
    }
    r = http.request('GET', setting['url'], fields=query)
    if r.status == 200:
        return r.data.decode('utf-8')
    else:
        return None

def ui_initialize(text):
    global v
    v['button3'].title = setting['source']
    v['button4'].title = setting['target']
    if text is not None:
        v['textview1'].text = text
        translated = translate(text)
        if translated:
            v['textview2'].text = translated

def get_setting():
    with open('setting.json', 'r') as f:
        setting = json.load(f)
    return setting

def save_setting():
    with open('setting.json', 'w') as f:
        json.dump(setting, f, indent=4, ensure_ascii=False)

def switch_source_target(sender):
    global setting, v
    setting['source'], setting['target'] = setting['target'], setting['source']
    save_setting()
    
    v['button3'].title = setting['source']
    v['button4'].title = setting['target']

def switch_tv_1_2(sender):
    global v
    v['textview1'].text, v['textview2'].text = v['textview2'].text, v['textview1'].text

def push_translate(sender):
    global v
    text = v['textview1'].text
    translated = translate(text)
    if translated is not None:
        v['textview2'].text = translated

def push_source(sender):
    global setting, v
    source = dialogs.list_dialog(
        'Source を選択',
        setting['langs']
        )
    if source:
        setting['source'] = source
        save_setting()
        v['button3'].title = setting['source']

def push_target(sender):
    global setting, v
    target = dialogs.list_dialog(
        'Target を選択',
        setting['langs']
        )
    if target:
        setting['target'] = target
        save_setting()
        v['button4'].title = setting['target']

def add_lang(sender):
    global setting
    lang = console.input_alert(
        '言語を追加',
        '追加する言語を入力してください',
        '', '追加'
        )
    if lang:
        setting['langs'].append(lang)
        save_setting()

class MyView (ui.View):
    def __init__(self):
        pass

    def touch_began(self, touch):
        # Called when a touch begins.
        for subv in self.subviews:
            if isinstance(subv, ui.TextView):
                subvo = ObjCInstance(subv)
                if subvo.isFirstResponder():
                    subvo.resignFirstResponder()

if __name__ == '__main__':
    main()

translation2.pyui

[
  {
    "nodes" : [
      {
        "nodes" : [

        ],
        "frame" : "{{122, 183}, {103, 32}}",
        "class" : "Button",
        "attributes" : {
          "uuid" : "7AC2C5BA-AD24-4311-AD01-BD9DC88DA443",
          "name" : "button5",
          "font_size" : 15,
          "corner_radius" : 0,
          "frame" : "{{80, 224}, {80, 32}}",
          "tint_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "border_width" : 0,
          "title" : "上下の文を入替",
          "action" : "switch_tv_1_2",
          "class" : "Button",
          "flex" : "LRTB"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{104, 6}, {33, 32}}",
        "class" : "Button",
        "attributes" : {
          "font_size" : 15,
          "flex" : "LR",
          "action" : "switch_source_target",
          "frame" : "{{80, 104}, {80, 32}}",
          "tint_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "title" : "",
          "uuid" : "B4106DF0-ED67-436B-977C-1B445BACBDE3",
          "class" : "Button",
          "name" : "button1",
          "image_name" : "iob:arrow_swap_24"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{6, 46}, {47, 32}}",
        "class" : "Label",
        "attributes" : {
          "name" : "label1",
          "frame" : "{{45, 104}, {150, 32}}",
          "uuid" : "3E5AD784-7D70-49A7-9A29-D29C4A22D849",
          "class" : "Label",
          "alignment" : "left",
          "text" : "原文：",
          "font_size" : 16,
          "font_name" : "<System>"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{20, 86}, {205, 90}}",
        "class" : "TextView",
        "attributes" : {
          "uuid" : "1A2CD453-9CAF-4B9C-B95B-192BBD91C1C3",
          "font_size" : 17,
          "corner_radius" : 5,
          "frame" : "{{20, 20}, {200, 200}}",
          "border_color" : "RGBA(0.840531,0.840531,0.840531,1.000000)",
          "editable" : true,
          "border_width" : 1,
          "alignment" : "left",
          "autocorrection_type" : "default",
          "font_name" : "<System>",
          "spellchecking_type" : "default",
          "class" : "TextView",
          "name" : "textview1",
          "flex" : "WHB"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{6, 183}, {47, 32}}",
        "class" : "Label",
        "attributes" : {
          "name" : "label2",
          "flex" : "TB",
          "frame" : "{{45, 104}, {150, 32}}",
          "uuid" : "8CCF6367-09C9-49AA-9669-8371F4418DD7",
          "class" : "Label",
          "alignment" : "left",
          "text" : "翻訳：",
          "font_size" : 16,
          "font_name" : "<System>"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{20, 223}, {205, 120}}",
        "class" : "TextView",
        "attributes" : {
          "uuid" : "2BA59F1B-9ED7-46C9-BB05-712A80D34599",
          "font_size" : 17,
          "corner_radius" : 5,
          "frame" : "{{20, 20}, {200, 200}}",
          "border_color" : "RGBA(0.842228,0.842228,0.842228,1.000000)",
          "editable" : true,
          "border_width" : 1,
          "alignment" : "left",
          "autocorrection_type" : "default",
          "font_name" : "<System>",
          "spellchecking_type" : "default",
          "class" : "TextView",
          "name" : "textview2",
          "flex" : "WHTB"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{84, 183}, {72, 32}}",
        "class" : "Button",
        "attributes" : {
          "font_size" : 15,
          "flex" : "LRTB",
          "action" : "push_translate",
          "frame" : "{{80, 224}, {80, 32}}",
          "tint_color" : "RGBA(1.000000,1.000000,1.000000,1.000000)",
          "title" : "翻訳",
          "uuid" : "05B8D6F5-48CE-45A0-ADF5-B305C1097599",
          "class" : "Button",
          "background_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "name" : "button2",
          "image_name" : "iob:arrow_down_a_24"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{16, 6}, {80, 32}}",
        "class" : "Button",
        "attributes" : {
          "uuid" : "652AF94D-5113-45C5-828C-21F279F4F79F",
          "font_size" : 15,
          "corner_radius" : 0,
          "frame" : "{{80, 224}, {80, 32}}",
          "tint_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "border_width" : 0,
          "title" : "Button",
          "action" : "push_source",
          "class" : "Button",
          "name" : "button3",
          "flex" : "LR"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{145, 6}, {80, 32}}",
        "class" : "Button",
        "attributes" : {
          "uuid" : "8153F20A-32D8-4787-8240-67DB708C3613",
          "font_size" : 15,
          "corner_radius" : 0,
          "frame" : "{{80, 224}, {80, 32}}",
          "tint_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "border_width" : 0,
          "title" : "Button",
          "action" : "push_target",
          "class" : "Button",
          "name" : "button4",
          "flex" : "LR"
        },
        "selected" : false
      },
      {
        "nodes" : [

        ],
        "frame" : "{{76, 46}, {89, 32}}",
        "class" : "Button",
        "attributes" : {
          "uuid" : "B917833A-811A-4EAC-8AAE-DBB7A9D5F359",
          "font_size" : 15,
          "corner_radius" : 5,
          "frame" : "{{80, 224}, {80, 32}}",
          "tint_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "border_width" : 1,
          "border_color" : "RGBA(0.000000,0.474510,1.000000,1.000000)",
          "title" : "言語を追加",
          "action" : "add_lang",
          "class" : "Button",
          "name" : "button6",
          "flex" : "LR"
        },
        "selected" : false
      }
    ],
    "frame" : "{{0, 0}, {240, 480}}",
    "class" : "View",
    "attributes" : {
      "flex" : "",
      "custom_class" : "MyView",
      "enabled" : true,
      "tint_color" : "RGBA(0.000000,0.478000,1.000000,1.000000)",
      "border_color" : "RGBA(0.000000,0.000000,0.000000,1.000000)",
      "background_color" : "RGBA(1.000000,1.000000,1.000000,1.000000)",
      "name" : "Google翻訳"
    },
    "selected" : false
  }
]

コード.gs

function doGet(e) {
  var p = e.parameter;
  var translatedText = LanguageApp.translate(p.text, p.source, p.target);
  return ContentService.createTextOutput(translatedText);
}