multilingual: Fix `styles.css` link when `defaultContentLanguageInSubdir = true`
multilingual: Fix `styles.css` link when `defaultContentLanguageInSubdir = true`

Fix #412

gcushen/hugo-academic,gcushen/hugo-academic,gcushen/hugo-academic,UltraCoderRU/hugo-academic,UltraCoderRU/hugo-academic,gcushen/hugo-academic