Is it okay to use multiple degree-intensifiers in a sentence?
Is 真的  really an intensifier?
我真的不知道(O)... 我真的很不知道 (X)
真的 (really) is an adverb for adjective that doesn't describe 'degree' but 'trueness'.

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我很强 (O)... 我强 (X)
&quot;很强&quot; can be translated as &quot;strong&quot; or &quot;very strong&quot; in English
&quot;很厲害&quot; can be translated as  &quot;awesome&quot; or &quot;very awesome&quot; in English
&quot;他的聲音真的很厲害&quot; should be translated as &quot;His voice is really awesome&quot;
If you translate it as &quot;His voice is really very amazing&quot; that would sound odd in English.
If the sentence was &quot;他的聲音很厲害&quot; then you can translate it as &quot;His voice is very amazing&quot; or &quot;His voice is amazing&quot;

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Is it okay to use multiple degree-intensifiers in a sentence?

One intensifier at a time
他非常强壮 (O)
他極之强壮 (O)
他非常極之强壮 (x)
他非常强壮，極之聪明  (O)