1) There are many xml and xsl files in Service Catalog installation folder so to narrow down to the file (s) with the problem:
1.1) Search for files that have modified recently by following the instructions on the following link: http://www.howtogeek.com/219157/how-to-easily-view-recently-modified-files-in-windows/
2.2) Narrow down the issue by testing behavior with different languages. Set the browser to different languages and log into Service Catalog and see if the issue is specific to one language. Based on the results, you can narrow down the issue to specific language folder. Example: If the issue is with Spanish language only, you need to search for the wrong file in the iceses folders like: USM_Folder\filestore\custom\locale\iceses and USM_Folder\view\webapps\usm\locale\iceses
2) In the xml or xsl file, search for <option> tags and search for the </option> closing tag for each one. Example: In the following screenshot there is a missing </option> tag in the category.xml:
3) Add the missing </option> tag to close the <option> tag.
4) Save changes, log out from Catalog and log into the application again. This time the issue will be solved.