Use latin script languages whitelist

Summary:
This commit reapplies 18e85899475e, reverted in e1af61f2d3ee.

A fatal issue was caused by relative/absolute path: Dæghrefn lives
in ~/eggdrop directory, scripts in ~/wikidata-access-layer, with
symlinks in ~/bin.

This change computes the correct path to l10n/ folder.

Test Plan: Same than in D523, but in another directory.

Reviewers: Ash-Crow

Differential Revision: https://devcentral.nasqueron.org/D525