は～くらいです

[topic] は [X] くらいです means "about the only one is X", "that's about it": the topic covers very little beyond X. くらい goes straight after a noun or a verb in the dictionary form, and the topic is often a whole phrase ending in のは or ことは.

ぐらい works the same way: えいご英語ぐらいです.

With and without くらい

Without くらい the sentence just states a fact. With it, the speaker plays the answer down: there is nothing much else.

くらい or しか～ない

しか with a negative says "only" flatly and shuts out everything else. くらい leaves a little room and sounds softer, which makes it the modest way to talk about yourself.