In sefTranslate, the tools for site translate ordasoft.com/sef-translate-joomla-translation-component
JQuery works also with help Translate API, so when you use jQuery - you use self Quota.
Some time before Google translate API - was free. So SefTranslate used only it. for site translate
We used Google translate API for Redirect and for jQuery
Next Google start asked money, so we start give possibility to our clients use Bing Translate API, It was full free.
Now Bing translate API - give free small quota on site translate.
Next Google created "Free widget for site translate", It is not API, but we give to our clients possibility use it for site translate