iFrame localisation

All API endpoints support url parameter lang to specify language for rendering visible texts:

Param	Presence	Value	Description
`lang`	OPTIONAL	`String`	url parameter to request a preferred language in ISO 639-1 format for rendering visible texts. If a specified language is not supported, by default text will be rendered in English. Examples: `.../authorize?lang=en` `.../authorize?lang=en-us`

Parameter value is saved in a browser cookie and is used for succeeding calls in cases where lang parameter is omitted.
Language can be provided in multiple formats:
- Only [language code] ( en, de, fr )
- Full ISO 639-1 [language code]-[region code] format ( en-en, en-us, de-at)
- In case of full format, only language code is taken into account.
Languages supported in ZealiD CSC API:
- en (English, default)
- de (German)
- fr (French)
Alternatively language can be set by calling separate endpoint /set_lang/<lang value>, for example ../set_lang/en