If you're Android-only, then the Android resource system is the most performant and easiest option for translated strings. Otherwise you can use anything you like; for our app, I wrote a thing to generate Kotlin code from a TOML file that picks a string based on the locale.
For colors and dimensions, Kotlin code is the ideal place to put them, because it doesn't make a whole lot of sense to change those based on Android resource configurations. MaterialTheme is a good example to follow; you could make your own analogous thing for common dimensions, or even just an Object with fields or Composable functions.
I would shy away from centralizing dimens in Compose, because dimens are very contextual in their usage. Usually you see a Composable UI element define a ThingDefaults object with some values that make sense, which are used as default values for the Composable function arguments. Button is an example that uses that pretty extensively.