could be Tuyuca, of the eastern Amazon,

based on the article Tongue twisters – In Search of the world’s hardest language, published by The Economist.

For some learners of German, this might come as a surprise. The der/die/das phenomenon for genders is hair-raising enough, and just recently, an adult student, close to the brink of giving up, exclaimed: Es ist leichter einen neuen Mann zu finden als Deutsch zu lernen (It is easier to find a new husband than learning German).

Well, she is still married and passed her German proficiency test.

Mark Twain had a lot to say about learning German too – read more at Life is too short to study German.

Well, enjoy reading these articles and be grateful you do not have to study Finnish with its 18 cases.

Or Tuyuca, which has only 1000 speakers left.