iOS applications can be translated into many languages, including custom ones, while iTunes Connect supports only a limited selection of these languages.
Here’s the full list of the supported languages:
English (U.S.) (en-US)
Chinese (Simplified) (zh-Hans)
Chinese (Traditional) (zh-Hant)
Danish (da)
Dutch (nl-NL)
English (Australia) (en-AU)
English (Canada) (en-CA)
English (U.K.) (en-GB)
Finnish (fi)
French (fr-FR)
French (Canada) (fr-CA)
German (de-DE)
Greek (el)
Indonesian (id)
Italian (it)
Japanese (ja)
Korean (ko)
Malay (ms)
Norwegian (no)
Portuguese (Brazil) (pt-BR)
Portuguese (Portugal) (pt-PT)
Russian (ru)
Spanish (Mexico) (es-MX)
Spanish (Spain) (es-ES)
Swedish (sv)
Thai (th)
Turkish (tr)
Vietnamese (vi)