so this one was a bit tricky for me and i know in the case of someone asking you would use ga because they would establish the topic, but if i were to just say my japanese is bad would i say wa or ga? i know ga is used to descibe but bad is an adjective not a verb such as like or dislike or want so im not sure and i think you would use wa otherwise
If it is just a statement, you can use は. Here is the basic sentence pattern.
(Topic) は (description)です。
わたしのにほんごは わるいです。(WATASHI NO NIHONGO WA WARUI DESU) = My Japanese is bad.
However, if you want to stress わたしのにほんご (my Japanese), が can be used instead of は.
(Example conversation) A: わたしのにほんごは わるいです。(WATASHI NO NIHONGO WA WARUI DESU) = My Japanese is bad. B: え？わたるのにほんごですか。(E? WATARU NO NIHONGO DESUKA) = What? Wataru's Japanese (is bad)? *WATARU is a boy's name. A: いいえ。わたしのにほんごが わるいです。(IIE. WATASHI NO NIHONGO GA WARUI DESU) = No. MY Japanese is bad.
"Using は and が to stress" is explained in Course 1 Lesson 7 (Grammar Part: 3). Please remember that emphasis usually occurs when something is said in contrast to a prior statement.
As for your example sentence, Japanese people don't really use わるい (WARUI/bad) when they talk about their English skills. Here are some common expressions.
1)わたしのえいごは よくないです。(WATASHI NO EIGO WA YOKUNAI DESU) = My English is not good. - sounds negative
2)わたしは えいごが とくいじゃないです。 (WATASHI WA EIGO GA TOKUI JANAI DESU) = I am not good at English.
3)わたしのえいごは まだまだです。(WATASHI NO EIGO WA MADAMADA DESU) = My English still has a long way to go./My English is not there yet/not good enough. - sounds reserved