Hello

I'm afraid you cannot do this.

What you would need to do is to export, create a new TB and import the content.

Unknown said:

I tried using Glossary Converter, but it produces a .sdltb with "nl", rather than "Dutch".

Did it stop at the place where you can change the languages or did it automatically convert without asking?  There is a flag for this:

Maybe that's your problem?

It did stop at a dialogue, which said:

But if I click on OK, it produces a TB with these languages:

Was there a way to change "nl" into "Dutch" back in that dialogue?

I managed to devise a workaround, by manually editing the file in Emeditor, as follows:

… which produces the desired result.