Translation:a constructed language
Hi Lee, yes you are right. the -bogh suffix makes a relative clause. So whenever you see -bogh be on the look out for what in English would use who, whom, whose, which, that, the silent/elided that, wherein, wherefore, or other relative pronouns and relative adverbs.
So basically you are looking at "a language WHICH has been constructed" which more simply is equivalent to "a constructed language".
You could use this to say, "Klingon is a constructed language": Hol chenmoHlu'pu'bogh 'oH tlhIngan Hol'e'. Or less succinctly but more literally, "As for Klingon, it is a language which has been constructed". As you can see you could totally throw out chenmoHlu'pu'bogh and then you would just have "the Klingon language is a language" or Hol 'oH tlhingan Hol'e'. It works pretty similar to how the same constructions work in English although I think maybe more like how they work in Japanese because of the differing word order.
I hope I did that correctly. I am still figuring out -bogh myself. I have meant to make a mini study of it but have not gotten to it yet. Luckily we have some incredible experts here to fix and add to this so thank you for this great learning opportunity with your question.