The phrase in the passage reads: "...it is normal to transfer the patterns of an indigenous language to those of a foreign language." Here, "those" functions as a placeholder to avoid repetition, referring back to "patterns." The passage says that the patterns of an indigenous language are transferred onto the patterns of a foreign language. In other words, a speaker may bring patterns (such as pronunciation, intonation, and grammar) from their native language into the new, foreign language they’re learning. So, "those" refers to "patterns of a foreign language"—the idea is that these indigenous language patterns are being transferred onto the foreign language patterns, affecting the way the speaker learns and uses the new language.