So um, hereās my tl;dr version:
Localizing is always good (at least not bad), specially when itās a clean fan translation. The fan makes it, you add it to the game, the fan gets credited, and everyoneās happy.
Defenderās Quest got many sale-boosts and promotions with the new localizing, as seen through the charts in the original post. It is also noticeable that a few months after a new localization was added, the sales were still considerably higher than no localized at all.
So sale-wise, a new language is always good, it helps alot people that donāt know English very well, and those people start buying the game (assuming they played the demo and didnāt understand any of the languages). And the earlier a localization is added, the more long-term sales are gotten (from the corresponding country).
And with this you learn that adding multiple language support to your games upon launch will boost their sales by a very high amount (may not be noticeably big in a single month, but will make a difference over time).
The End.
So, an even shorter form of that:
Localizing is never bad, it may not be good but it is never bad, so itās always worth a shot.
Localizing your game boosts its sales.
The earlier you localize, the higher the sales/promotions will be.
EDIT: Oh yeah and make sure localizing doesnāt cost too much, fan translation is always good too.