Kartli is a large region in central Georgia.
Outside of Tbilisi and Mtskheta, you should not expect to encounter anyone who speaks any European languages. Georgian is the principal language throughout most of Kartli, but there is a significant section of southern Kvemo Kartli (around Gardabani), where most residents are Azeri speakers and you may be able to communicate effectively with knowledge of Turkish. In South Ossetia, you should actually avoid speaking Georgian because of the intense ethnic conflict between the Georgians and the Ossetes, who speak Ossetian, in addition to Georgian and Russian. Speaking Russian is only useful and recommended in areas where ethnic minorities live. Among the ethnic minorities Russian is the regional lingua franca and is spoken by many older people, and also by many taxi drivers. The younger generation is increasingly speaking English due to hostility towards Russia, and also because English is taught in schools since independence and has replaced Russian as a second language in schools nation-wide. When in need for help, look for younger people, as they are more likely to know some English.