Add a `/public/langs.json` file that maps between Wikimedia language codes (ISO 639-1 or BCP 47?) to the different engine's codes (which will also indicate engine support for a language, and so we'll be able to switch the multiselect widget to only show the correct ones).
For example:
```lang=json
{
"en": {
"tesseract": "eng",
"google": "en"
},
"bn": {
"tesseract": "ben",
"google": "bn"
},
"uz": {
"tesseract": "uzb",
"google": "uz"
},
"uz-cyrl": {
"tesseract": "uzb_cyrl",
"google": "uz-Cyrl"
},
"he": {
"tesseract": "heb",
"google": "iw"
},
"it_old ??": {
"tesseract": "ita_old",
}
}
```
This way, we'll be able to display a localized list of available langauges in the wiki UI.
Outstanding question: how do we deal with language codes such as `ita_old` which don't have direct mappings in ISO639-1?