You can make the naming practices of the people of your setting obvious, with a little repetition. Not even knowing their language, if I see the same suffix or lead word on all rivers' names, I'll get the idea that bit *means* "river". Label some obvious settlement size symbols in the key, say yabba, dabba, and due (big to little) and I'll know when I see a big city name Something-due I'll have an idea that during the tenure of the current language it probably grew from town to city.

That said, a little such goes a long way on a map. No matter how well thought out the language you have crafted, you don't want to force your map user to do a lot of decoding; that'll get in the way of understanding when you were trying to *transmit* information. The extreme case of this is where an entire map is labelled in a ' local script' unfamiliar to the reader. Such winds up being an 'art piece' instead of a functional map; one can glean some from the graphical elements alone, and certainly the *flavor* of the setting can be conveyed... If you really want to do a lot of in-character labeling like that, consider tossing the reader/ players/ users a bone, and "scribbling in" some pronounceable or even real-world annotations. That way you can have the beauty of say the elvish original, but the apt or snarky remarks of the human who took notes can carry whatever info is crucial to the user.