Linguistic difference was mapped directly onto presumed racial difference.

Evidence

It was assumed that if languages were as distinct from each other as the linguists said they were, then too the language users—their minds, cultures, potentials, and even their bodies—were different in similar ways. And these distinctions had the force of ontological, empirical truth behind them, together with the convincing demonstration of such truth in studies of origins, development, character, and destiny. — Edward W. Said, Orientalism, 586

Categorization

• XREF: The linguistic-racial slippage is a precursor to Orientalism’s central operation of collapsing speech, mind, and body — carry into later readings on representation of the ‘Other’.
• corroborated: 2 independent passages support this claim — Edward W. Said, Orientalism, 586