Um, or better yet you could practice translating real Japanese... look up some RAW manga, most of 'em have furigana anyway
And actually it's
easier to translate with kanji. Here's a good dictionary with example sentences to help ya with your studies
Tangorin Japanese Dictionary
なぜ、
にほんご を
べんきょう する の です か。
なぜ、
日本語 を
勉強 する の です か。
Edit; Have some fun reading practice here;
School Expressions by Scene｜アニメ・マンガの日本語 Japanese in Anime & Manga