This has been long pending. We always wanted to to open source the XLIFF connector for Adobe Experience Manager 6.1, but have been really busy. The connector was built for Adobe Experience Manager 6.1 and is listed on the Adobe Marketing Exchange here. The connector was always free and anyone could download the connector from Adobe Marketing Exchange. The connector was also featured in Multilingual Magazine. Today, we are open sourcing the source code. You can look at the source code here: https://github.com/ExperienceLabs/xliff-export-connector
For core XLIFF conversion, connector relies on the OKAPI framework. It supports both XLIFF 1.2 and XLIFF 2.0 conversion. In case, you have forked OKAPI and have a modified version, you can just replace the OKAPI libs and repackage the connector.
In Adobe Experience Manager 6.2, Adobe has improved XLIFF support. Interestingly enough, they did not go ahead and implement XLIFF conversion. Rather they defined an interface and rely upon customers to implement the interface (basically write an XLIFF conversion). The XLIFF interface is modeled on Translation API. You can repurpose the XLIFF connector to build a connector for AEM 6.2 by implementing the interfaces as exposed in AEM 6.2. I want to do the same, but will park that as weekend project for later. I will share with you more once I get around implementing it myself.