Are not synonymous.
But they are are related.

It takes a compassionate eye
To see through the self-effacing habits
Of the quiet brilliant ones among us.
Not everyone who holds silence
Has nothing to say,
And many of those who fill up space
Do so in service of themselves.

When it comes to a language that
One may not be confident in speaking,
Those that stumble and hold back
Can easily be mistaken
As not knowing the language at all.
And confidence (or the lack of it)
Self-fulfils;
Those with it, tend to become more competent
And those without can suffer diminishing fluency.

So it follows, then,
That there is little benefit in shaming someone
For not being fluent in a language,
As this puts a dent in their confidence
Which undermines their competence.

Confidence and competence

Are not synonymous.
But they are are related.