In German it is easy. Basically, within a syllable, an "h" after a vowel is mute as well, it only means that the vowel before it is pronounced as a long vowel.

Rum (u pronounced like in Spanish: rubia) = rum (from Jamaika or elsewhere)
Ruhm (u pronounced like in English: room) = glory

But of course, we have also got long vowels which when written are not followed by an "h". Languages shouldn't be too easy.