cs-CS language is being changed by cs-RS

[Tominka]

Hello,

since i have been using Angular 18, i´ve got issue with languge key cs-CS.
Library is finding loaded cs-CS sources under cs-RS language.

Testing code:

Console output:

I tried a lot of ways. Only way is change cs-CS across the project to cs-RS, but it is not solution an i need to have it correctly.
Should it be a library bug?