"I drink under the wet umbrella."
Translation:A nedves esernyő alatt iszom.
It isn't - it's using the indefinite conjugation endings for an "ik" verb, as iszik is an "ik" verb.
The én form happens to have -em, -om which coincidentally looks like the definite conjugation ending for non-"ik" verbs. That's not usually a problem since most "ik" verbs are intransitive and can't take an object, so they're never used in the definite conjugation anyway.
The need to distinguish "ik" from non-"ik" verbs may be one of the reasons that dictionary list verbs by their third person singular form, e.g. iszik, rather than by the infinitive.