Language code with a hyphen not allowed in Add Translation for contents menu

When using the Add Translation feature, I’m not allowed to type a language code with a hyphen. My BCP-47 language code has a hyphen. I had to resort to editing the .def file. This happened in SAB 9.3, but I’m guessing the problem is in 10.0 also.

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Yes it should allow a hyphen so you can set up two translations in different scripts.
I have written it up.