These are some of the initial possibilities about Windows 10 supported languages . After constant updates, things always change. Later, it will probably be possible to install more languages.
Windows 10 supported languages (Windows 10 for Mobile & Desktop )
Windows 10 Arabic language
Windows 10 Catalan language
Windows 10 Czech language
Windows 10 Dutch language
Windows 10 English (UK)language
Windows 10 English (US)language
Windows 10 Finnish language
Windows 10 French (Canada)language
Windows 10 French (France)language
Windows 10 German language
Windows 10 Hindi language
Windows 10 Italian language
Windows 10 Japanese language
Windows 10 Korean language
Windows 10 Polish language
Windows 10 Portuguese language
Windows 10 Russian language
Windows 10 Simplified Chinese language
Windows 10 Spanish (Spain)language
Windows 10 Spanish (Mexico/LatAm)language
Windows 10 Swedish language
Windows 10 Thai language
Windows 10 Traditional Chinese language
Windows 10 Turkish language
Windows 10 Vietnamese language