The Sordello who acts thus with language represents the action of Browning himself at the time he was writing the poem.

If so, the passage is full of interest.
All we know about Sordello as a poet is that he wrote some Italian poems.

Those by which he was famous were in Provencal.

In Dante's treatise on the use of his native tongue, he suggests that Sordello was one of the pioneers of literary Italian.

So, at least, Browning seems to infer from the passage, for he makes it the motive of his little "excursus" on Sordello's presumed effort to strike out a new form and method in poetic language.