我学了中文了 - is it a good sentence?
&quot;我学中文&quot; - &quot;I learn Chinese&quot;
&quot;我学了中文&quot; - &quot;I've learned Chinese&quot; [了 after a verb is a verb particle that indicates the verb is completed]
&quot;我学中文了&quot; - Depend on context, it can Imply &quot;我(開始)学中文了&quot; (I have started to learn Chinese) or &quot;我(肯)学中文了&quot; (I am willing to learn Chinese now).  了 after a verb phrase is a verb particle that indicates a change of situation. (change from not learning Chinese to learning Chinese or from unwilling to willing)
In &quot;我学了中文了&quot; (I've learned Chinese), the first 了 is a verb particle and the second 了 is a final particle.
A final particle is a particle placed at the end of a sentence to (a) indicate the sentence has ended (b) soften the tone of speech (c) to stress the sentence itself or add emotional tone to it.
&quot;我学了中文了&quot; is a valid sentence