First of all, if you would like to allow the users to translate offline, you need to have an Administrator role in order to enable such an option in Configuration → Settings → Translation → Workflow and access → Linguist general options → Allow linguists to download/upload.
Create a project in XTM Cloud (using any supported file extension).
Generate the XLIFF file in Project editor → Files → Offline translation.
After you generate the XLIFF file, you can download it by clicking the green arrow.
A generated XLIFF file can be translated in any text editor or used as a source file in another CAT tool that supports this format.
The finished translation file can be then reuploaded to XTM Cloud. Select in Project editor → Files → Offline translation,using the purple arrow this time.
At this stage, you can specify the workflow step to which you would like to upload your translation and specify what segments are to be approved immediately:
Note that if the file has been translated in another CAT tool, it is important to keep the XLF extension.
If you not want to the project to be translated outside XTM Cloud, you can always use the XLIFF file as a source file for the XTM Cloud project and translate that file in XTM Cloud.