However, the 'preposition + relative pronoun which' part has become the relative adverb 'where.'
Literal
However, preposition + relative-pronoun which [genitive-の] part [subject-が] relative-adverb where [state-となっています].
An English grammar explanation in Japanese. 前置詞 (ぜんちし, 'preposition'), 関係代名詞 (かんけいだいめいし, 'relative pronoun'), and 関係副詞 (かんけいふくし, 'relative adverb') are all grammar terminology. しかしながら ('however,' formal) is a written-register conjunction. ~となっている ('has become / is officially') uses the formal ~となる form. The English terms 'which' and 'where' appear in Latin script. A metalinguistic sentence about English grammar structure.