meckern
to complain
In colloquial language, to complain about something in a nagging or dissatisfied way.
Anstatt zu helfen, meckert er nur über die viele Arbeit.
Instead of helping, he just complains about all the work.

to complain / bleat
Loading your saved state.
to complain
In colloquial language, to complain about something in a nagging or dissatisfied way.
Anstatt zu helfen, meckert er nur über die viele Arbeit.
Instead of helping, he just complains about all the work.

The meaning depends on the subject. When a person 'meckert' (complains), they are complaining. When a goat 'meckert' (bleats), it makes its typical sound.
Mein Nachbar meckert ständig über den Lärm.
My neighbor constantly complains about the noise.
When someone complains about something, 'meckern' (to complain) is used with the preposition 'über' and the accusative.
Sie meckert immer über das Essen in der Kantine.
She always complains about the food in the cafeteria.
The word 'meckern' (to complain) in the sense of 'sich beschweren' (to complain) is colloquial. It sounds nagging and is unsuitable for formal situations or a polite complaint.
Hör auf zu meckern und hilf mir lieber!
Stop complaining and help me instead!
In the meaning of the goat sound, 'meckern' (to bleat) is an onomatopoeic word. The sound of the word imitates the sound it describes.
Auf dem Bauernhof konnte man die Ziegen laut meckern hören.
On the farm, you could hear the goats bleating loudly.
to criticize
'kritisieren' and 'meckern' can both mean that someone is not satisfied with something. 'kritisieren' is more neutral and can be objective: you name specific mistakes or problems. 'meckern' is colloquial and often sounds nagging or dissatisfied, sometimes without a good reason. Learners may confuse the words because both express negative reactions. If someone is talking about a problem seriously and with reasons, 'kritisieren' fits better. If someone is complaining and sounds rather bad-tempered, 'meckern' is more natural.

Luis meckert, weil die Hausaufgaben heute besonders lang sind.
Luis complains because the homework is especially long today.
Die Mitarbeiter kritisieren die neuen Arbeitszeiten, weil sie für Familien schwierig sind.
The employees criticize the new working hours because they are difficult for families.