Theme Check is a plugin that tests your theme with the latest theme review standards using automated testing tools. However, the results should be taken with care. Many items it will return may seem to be errors, but are not. Please see below for a description of things you will see in the results. Errors you may see in the test results do not mean that the theme is broken or will not work. Themecheck is a general guideline, and is not anywhere close to being fool proof.
1) text domain warnings: Theme Check plugin is listing these as false positives. The listed items are correct.
2) base64_encode: that is a normal php function. WordPress theme repo prohibits it for no reason in our opinion. You can do harmful things with any php code. It is officially allowed by ThemeForest!
3) file operations like fread, fwrite, fsockopen, fopen, fclose: all used only for importer. WordPress prefers using the WP_filesystem, but there is no problem with using the php functions.
4) file_get_contents: the main problem is that wp_filesystem offers very limited functions. So for example for revslider imports we use php ZipArchive class right now which allows you to read a file inside a zip without extracting the zip. The wp_filesystem function get_contents doesn’t allow to do this. So we would need to extract all the zips to the upload directory, then get the contents and then delete them again when finished. that causes a lot of overhead and is completely unnecessary.