Complex sentence: Young Janne Sibelius went to the Finnish-speaking "Hämeenlinna Normal-Lycee", which he attended from 1876 to 1885, but his first language remained Swedish all his life.
Split into simpler sentences: Young Janne Sibelius went to the Finnish-speaking "Hämeenlinna Normal-Lycee", which he attended from 1876 to 1885. But his first language remained Swedish all his life.