Can I use a chinese legend card and english runes, main deck + signarure cards?

Yes — that combination is legal.

Language rules apply per deck zone, not to the whole deck. Your Legend can be Chinese while your Main Deck (including Signature cards) and Rune Deck are English, since each zone just has to be internally consistent.

Two catches: your Chosen Champion is a Main Deck card, so it must be English like the rest of the Main Deck; and all 12 runes must be English — you can't mix Chinese and English runes together. Rule 420.1 allows official cards of any language, and the FAQ confirms the Legend is treated separately from the other zones.