The best and easiest way to translate Terraclassifieds is to use Loco Translate plugin.
You need to install this plugin simply as every Wordpress plugin. After installation and activation navigate to Loco Translate and choose Terraclassifieds in section Running plugins.
Now click on New language
In the next step choose your desired language for translation and location for language files ( the best option is to use Author - files located inside plugins directory ). Click on Start translating when you are ready.
Now you need to choose source text for translation, ex. Latest first and then enter the translation. Do it for every source text and then click Save when you are done.
That's it. Very, very simple. Your translation is now located in wp-content/plugins/terraclassifieds/languages directory. For French there will be files: terraclassifieds-fr_FR.mo and terraclassifieds-fr_FR.po.