RE: Select more Languages at Business Central
D365BC On-Premise:
Microsoft Dynamics 365 Business Central Server -> Choose Instance -> Clear Field "Supported Languages" -> Restart Instance
Supported Languages
Specifies which of the installed Dynamics 365 Business Central languages on the server instance will be available for use in the clients. If you do not specify a language, then all installed languages will be available. In the client, users can switch among the supported languages. The value is a semicolon-separated list that contains the language culture names for each language. For example, if you want client users to be able to choose among da-DK, en-US, and en-CA, set the value to da-DK;en-US;en-CA.
If you specify any languages in this setting, then you must include the language that you specified in the Default Language setting.
If there are application-specific configuration settings, this setting will be overridden by the supported language setting that is specified in application-specific configuration file
D365BC cloud:
https://admin.powerplatform.microsoft.com/environments
Select Environment -> Settings -> Languages -> Mark Languages and Apply