"Trink weniger Milch."

Translation: Drink less milk.

[Logicsama]

How do I express the nuance that English does in the following sentences
"Eat less meat" this less I think says "less quantity"
Versus
"Eat meat less"? This less I think says "less often"

Or am I getting it wrong in English as well :O

[mizinamo]

It would be the same in German, as the adverb goes after the verb in German - you can't express the other possibility by putting the adverb at the end.

You could explicitly say weniger oft "less often", of course, or use nicht so viel "not so much" versus nicht so oft "not so often".

[Justiniwini]

Why weniger and not wenige?

[mizinamo]

Why weniger and not wenige?

The -er is the comparative affix, turning wenig "little" to weniger "less".

As for why there is no gender/number/case ending (one might expect wenigere Milch with -e to agree with feminine accusative Milch) -- I think this is simply an exception to remember.

viel (much) also usually has no gender/number/case ending in the singular: ich trinke viel Milch "I drink a lot of milk", and mehr (more) never does: ich trinke mehr Milch als du "I drink more milk than you".