Even though some people allege that defining of terms is useless and unnecessary, It really depends on what you mean by “national language”.
If you mean, “everyone has to speak this language and no other…or else.” That’s one thing. If you just mean that all governmental business/documents/signs/statutes, etc. must be done/made available in some language, that’s a completely different thing.
I mean, I could start my own club and mandate an “official language”.