Learn Dutch: Desondanks eet ik wat slappe friet. - Nevertheless, I am eating some limp fries.

The sentence starts with the adverb Desondanks (Nevertheless). In Dutch main clauses, the verb must always take the second position. When something other than the subject is in the first position, the subject must move directly after the verb. This is called inversion.

I learned that wat means "what". Why is it translated as "some" here?

While wat means "what" in questions, it is very commonly used in statements as an indefinite pronoun meaning "some" or "a little". So wat slappe friet simply means "some limp fries".

Why does the adjective get an -e at the end (slappe instead of slap)?

Because friet is a de-word (de friet). Adjectives placed before nouns normally get an -e ending. The main exception is when the adjective comes before a het-word that has an indefinite article (like een) or no article at all (like with wat). Since friet is a de-word, it keeps the -e.

In English we say "fries" (plural). Why is friet singular here?

In Dutch, friet (as well as the regional alternative patat) is typically treated as an uncountable mass noun. You talk about it the same way you talk about "rice" or "pasta" in English, so it stays in the singular form even for a whole portion.