The content created with Content Translation gets evaluated against the filters of the local wiki (in the same way as any regular edit). Different wikis have a different set of filters to prevent vandalism but sometimes they misidentify legitimate content (they are specially sensitive to external links and new users).
Content translation will try to validate the translation as you edit and warn you about the issues in it identified by the filters of target language wiki. You will be presented with a warning card in the tools column of translation editor. It is recommended to fix the issue before publishing the translation.
How to fix the issues
The warning card in tools column will have information and links to detailed documentation of the issue.
Some of the issues are warnings, but some others will prevent you from publishing the translation as a new article. When you publish, Content Translation tool will inform you the publishing failed. This does not mean that your effort is lost. Your translation is always saved with Content Translation. The error message will have the details of the issue that prevented you from publishing. Try fixing it (or removing the suspicious content) and retry publishing. It will succeed.
In order to help other users not to have similar issues, you can report the problems you had for the administrators in charge of the filters to adjust them. Check the section below for further information.