nieprzekonujący Englisch:

His explanation is unconvincing.

The argument is rigorous and coherent but ultimately unconvincing.

The Allies made a very unconvincing attempt to help the Russians.

an unconvincing argment for increasing indirect tax

The explanation that Mark gave was rather unconvincing.

They gave some unconvincing explanations for the system failure.

your objections are unconvincing

The plot is very unconvincing, since Richardson's concern is only with characterization and nothing else.

an unconvincing smile

How many times have I explained to you that your explanation is most unconvincing?