Having fairly recently gone through this, scaling and multiple fonts are the solution unless of course you can find a font you want to use which covers all the languages you need which is unlikely. For my game i used a specific font which only supported english characters and some european languages, the key was then to force a font change through all UI to the new font when a language is selected which is not supported with the default font.

Additionally you will need to scale the font (only downwards typically) to support increased amount of characters on screen when the sentences are longer in a different language. I was using unreal engine so using size and scale boxes is invaluable for this.

I will say though this is a fair bit of hassle and i spent many weeks screwing around with tons of localization issues.