You can't 'warm up' a language in English. It's a nice idea, but we don't say it.
We'd use 'practise', or say something like 'We chat every week to help her keep up her Chinese'.
If you want an idiom, we could say, for example '...to stop her Chinese getting rusty.' If you don't use machinery, it goes rusty. It's the same with languages.
We can also use the idiom 'brush up'. If you want to practise a language which you haven't used for a while, you can 'brush up your Chinese.' Like an old but serviceable coat that just needs a bit of TLC.