Tłumaczenie - Niemiecki-Angielski - Seine Leistungen sind um so ...

IMHO:
"His achievements/deeds are all the more admirable as he has performed them under difficult circumstances"

Can it be?

I agree with Lev van Pelt's translation.
The original means "he did (those) things under difficult circumstances, so they're even more admirable (that just in and of themselves)".
Merdogan's version means "the things that he does under difficult circumstances are even more admirable (than other things)".
I could see "performance" instead of "achievements" depending on what is talked about exactly.