If I ldd gettext.xs.dll, I find it has some unknown unresolved references

I don't understand the ldd output, but yours looks pretty normal compared to other 64-bit strawberry xs.dlls that are not troublesome. For example, for lib/auto/Win32/Win32.xs.dll, I'm seeing:

$ ldd.exe lib/auto/Win32/Win32.xs.dll
        ntdll.dll => /c/Windows/SYSTEM32/ntdll.dll (0x76db0000)
        kernel32.dll => /c/Windows/system32/kernel32.dll (0x76c90000)
        KERNELBASE.dll => /c/Windows/system32/KERNELBASE.dll (0x7fefc9
+d0000)
        ??? => ??? (0x64cc0000)
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What's the error message you're seeing when gettext.xs.dll fails to load ? (It's likely not very helpful ... but worth a try.)
Are there any pop-ups associated with the failure ? If so, what message so they provide ?

When I want to build an import library from a dll, I start with gendef.exe (which ships with strawberry) and use it to create a def file:

gendef -a mydll.dll
then, using the generated mydll.def:
dlltool --kill-at --input-def mydll.def --output-lib libmydll.a
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I don't know if that is what you need, or if it will provide better mileage than VinsWorldcom's method using pexports.

If you're using MSYS2 dlls, you'll want the ones that are in the mingw64\bin - and then you might as well just use the associated import lib (.dll.a) in the mingw64\lib folder.
The mingw64\lib folder also probably provides static (.a) libs if you want to avoid the dll dependency.

Cheers,
Rob