The more common definition of “linguist” is effectively “translator”, i.e. someone who is a native speaker of language X but can also speak language Y. That’s also the military definition.

In terms of the study of linguistics, in academia you can have a great many “linguists” who are not translators but are versed in the science of linguistics and can e.g. do grammatical analysis. It’s an entirely different skillset from “translator”, and in fact, one doesn’t need to speak language Y to do it.

So, mostly I’m differentiating myself from the translator-type linguist and saying I’m the linguistics-type linguist. And because I also do that for a living, I added professional.