"I drink a good tea."
Translation:Ich trinke einen guten Tee.
You use the -e ending for adjectives ("gute") in these instances:
1) When paired with any definite article (der, die, das) in the nominative case or any of the so-called "der-words" (dieser, jeder, jener, etc.) in the nominative:
der gute Mann; die gute Frau; das gute Kind dieser gute Mann; diese gute Frau; dieses gute Kind
2) When paired with any der-word + feminine or neuter noun in the accusative (which look identical to their nominative forms):
jede gute Frau, jedes gute Kind
3) When there's no article attached, you need to show the noun's gender and case with the proper ending for the adjective, so if it's feminine (nom. or acc.):
gute Frau, kleine Schwester, rote Blume, etc.
4) When paired with feminine nouns with an indefinite article ("eine") or other "ein-words": "keine", "meine" etc.
Eine Kleine Nachtmusik, keine gute Pizza
As for -en, it's the ending used for adjectives when paired with any article, "der-word," or "ein-word" that isn't one of the above examples.
So consider these sentences:
Ich trinke den guten Tee.
Ich trinke einen guten Tee.
Ich trinke diesen guten Kaffee.
Ich trinke meinen guten Kaffee.
In each example we have a masculine noun in the accusative case, so the adjective takes -en.
What a very strange way to refer to drinking tea. Sounds unnatural to say "I drink a good tea"
- Are you also drinking Bancha?
- No, I don't like that cheap stuff. I drink a good tea.