You can download the 2.0 version from our site or update it from Joomla. You can check the documentation about the update. Make sure to take a backup of your site. However, if you update the sellacious, you won't have an issue with the language file.
I couldn't find the file en-GB.tpl_squick.ini. and have searched in few different folders. I have tried to update the system manually by following the instructions and upload the files but it did not work well and my website went down. I ended up restoring the database and website files to bring my website back to live. Also, I tried to update via Joomla but had the following error as you can see on the attached image.
Could you help me by any chance by having a look at my website? I meant for the missing language string and possibly updating?
I suggest you use the latest version of sellacious, which has many more features like SMS, chat between sellers/buyers, updated Delivery/Pickup Extension, Hyperlocal, etc. You can check the demo here. https://demo.sellacious.com/squick
As for the language key, go to language/en-GB/en-GB.tpl_squick.ini. Check the folder of the language you are using on your site.
I am using SQuick - Starter eCommerce Template and there is not Language folder for it. I went through the address URL you told me and have not found language folder. My sellacious version looks like 1.7.3
You can manage this key in the ROOT/templates/TEMPLATE_NAME/languages/en-GB/LANGUAGE FILE.