1. To be likely to change at any time. English = (be) variable.
2. To change in size, amount, or degree; for one thing to change in size, amount, or degree when another thing changes. English = vary.
3. Of a person's mental or physical state, to be constantly changing from better to worse. Overall, it is not very good. Idiomatic English = (be) up and down, (be) so so, (be) fifty-fifty.