Complex sentence: For the most part, Gothic is known to be significantly closer to Proto-Germanic than any other Germanic language except for that of the (scantily attested) early Norse runic inscriptions, which has made it invaluable in the reconstruction of Proto-Germanic.
Split into simpler sentences: For the most part, Gothic is known to be significantly closer to Proto-Germanic than any other Germanic language, except for that of the (scantily attested) early Norse runic inscriptions. This has made it invaluable in the reconstruction of Proto-Germanic.