I like free online quizzes and tests, but they aren’t really worth anything unless they’re good.  At least some of these from language-learning company Transparent Language seem pretty good! And plentiful: they are available for more languages than are listed here, and there are often multiple resources per language.

I haven’t done a thorough examination of the quizzes yet—I merely tried out a little of the Dutch and Portuguese—but I think you could have a nice time roaming about here.

One warning: materials for languages with different writing systems generally appear to be offered only with romanization. The only exception I came across was with the Russian materials. Greek, Japanese, Arabic, Chinese, Persian (which you will find under Farsi): all romanized. 

For some of the more popular languages, you can play around with quite a few different quizzes and exercises. Even for Irish, which does not quite qualify as a world language, Transparent Language has posted a number of free tools.

Besides the quizzes, which are divided up into three different categories based on which of Transparent Language’s products they correspond to, there are also free online proficiency tests. Fun!

The tests are available for 12 languages, including Mandarin (in pinyin), Swedish, Latin, and even Irish. You don’t have to relinquish an e-mail address or any personal information to take these tests, but if you did want to consider signing up for a Transparent Language online course, you could officially submit your results once you finished.

I am not familiar with Transparent Language’s paid products and services, so I can’t offer any guidance on those.