Thanks for contacting WPML forums support. I'll be glad to help you today.
1) Please let me know which string you want to translate and how this string is added to the default language.
2) It's not related to the issue, but according to your Debug.info, the WP memory limit needs to be increased. PHP memory is fine, but WordPress uses 64Mb as default. The minimum requirements for WPML are 128 MB. (Kindly check this page https://wpml.org/home/minimum-requirements/)
You can increase it by adding the following code in your wp-config.php file right before the /* That's all, stop editing! Happy publishing. */ line: