Steps to add new language:

1. Create a folder in static/ui with you languages two letters code.
2. Copy interface.json from static/ui/en to your newly created folder.
3. Translate interface.json strings to your language.
4. Add you language data in static/ui/languages.json

Example:

"ar": {
    "name": "Arabic",
    "momentLocales": "ar",
    "currency": "USD",
    "unicode" : "🇸🇦",
    "buttonColor": "#2196F3"
}

You can get momentLocales and language code for your language check:

• af (Afrikaans)
• ar-dz (Arabic - Algeria)
• ar-ly (Arabic - Libya)
• ar-ma (Arabic - Morocco)
• ar-sa (Arabic - Saudi Arabia)
• ar-tn (Arabic - Tunisia)
• ar (Arabic)
• az (Azeri)
• be (Belarusian)
• bg (Bulgarian)
• bn (Bengali)
• bo (Tibetan)
• bs (Bosnian)
• ca (Catalan)
• cs (Czech)
• cy (Welsh)
• da (Danish)
• de-at (German - Austria)
• de-ch (German - Switzerland)
• de (German)
• el (Greek)
• en-au (English - Australia)
• en-ca (English - Canada)
• en-gb (English - Great Britain)
• en-ie (English - Ireland)
• en-nz (English - New Zealand)
• en-us (English - United States)
• es-do (Spanish - Dominican Republic)
• es (Spanish)
• eu (Basque)
• fa (Farsi - Persian)
• fi (Finnish)
• fo (Faroese)
• fr-ca (French - Canada)
• fr-ch (French - Switzerland)
• fr (French)
• gd (Gaelic)
• he (Hebrew)
• hi (Hindi)
• hr (Croatian)(
• hu (Hungarian)
• hy-am (Armenian)
• id (Indonesian)
• is (Icelandic)
• it (Italian)
• ja (Japanese)
• ka (Georgian)
• kk (Kazakh)
• km (Khmer)
• kn (Kannada)
• ko (Korean)
• lo (Lao)
• lt (Lithuanian)
• lv (Latvian)
• mk (Maori)
• ml (Malayalam)
• mr (Marathi)
• ms-my (Malay - Malaysia)
• ms (Malay)
• my (Burmese)
• nb (Norwegian)
• ne (Nepali)
• nl-be (Dutch - Belgium)
• nl (Dutch)
• pa-in (Punjabi)
• pl (Polish)
• pt-br (Portuguese - Brazil)
• pt (Portuguese)
• ro (Romanian)
• ru (Russian)
• sd (Sindhi)
• sk (Slovak)
• sl (Slovenian)
• sq (Albanian)
• sr-cyrl (Serbian - Cyrillic)
• sr (Serbian)
• sv (Swedish)
• sw (Swahili)
• ta (Tamil)
• te (Telugu)
• th (Thai)
• ttl-phh
• tr (Turkish)
• uk (Ukrainian)
• ur (Urdu)
• uz-latn
• uz (Uzbek)
• vi (Vietnamese)
• yo (Yoruba)
• zh-cn (Chinese - Simplified)
• zh-hk (Chinese - Hong Kong)
• zh-tw (Chinese - Taiwan)