WishList Member includes a language pack so you should be able to edit the text.
Here are the steps needed to translate WishList Member:
Translating WishList Member
I. Create the correct language file
1. Download poEdit at www.poedit.net
2. Download the file lang/wishlist-member-en_US.po (from wishlist-member plugin folder of your site)
3) Open the wishlist-member-en_US.po file in poedit software.
4. Click File -> Save As and change en_US to your language. (example: wishlist-member-de_DE.po for German)
6. Click File -> Save
This now generates the correct .po and .mo files for your language.
II. Tell WordPress to use your language file
1. Upload translated .po and .mo file back to the lang folder of wishlist-member plugin for your site.
2. You need to set the language under WP options.
You can translate or change words, sentences or messages, by using the poedit program.
Note: It is easier to search for a specific word within a sentence when looking to translate a full sentence.
After a translation has been completed, the site admin needs to upload BOTH po and mo files to the WishList Member lang folder.
The translation will not work if just the po file is uploaded. The po file is for poedit when translating WishList Member and the mo file is for WordPress to use the translated words.
Poedit automatically updates the mo file when a site admin edits the po file.
This all means that a site admin needs to upload BOTH po and mo file.