How do you hyphenate "Lagrangian"?
Solution 1:
I would go your style guide.
The Chicago Manual of Style (CMoS, 13th ed.) says:
Word division. The fundamental principle of French word division is to divide as far as possible on a vowel, avoiding consonantal ending of syllables except where n nasalizes a preceding vowel:
a-che-ter
in-di-vi-si-bi-li-té
ba-lan-cer (not bal-an-cer)
ta-bleau (not tab-leau)
(Section 9.27)
While it is better to not divide a proper name, word division for a French word might be:
La-gran-gi-an