Looking on the internet deeply has found these results:

translation proficiency is the most popular phrase on the web.

translation competency 12,500 results on the web	translation proficiency 19,300 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
The same principle is also to apply to translation of certificates of competency.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

translation competency

12,500 results on the web

translation proficiency

19,300 results on the web

More popular!

The same principle is also to apply to translation of certificates of competency.

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.