Lower Sorbian is a lesser-resources Slavic language that is quite close to (Old) Polish.

Create a set of test sentences (see various pages of 'Pending tests' and 'Regression tests' on the Wiki) for translation between Lower Sorbian and Polish.

The tests should cover as many features of the languages as possible. Some of the examples might be able to be found in a grammar, others might need to be invented. This will not involve programming, only grammatical analysis.

You can find an example here for Czech and Polish.