"is dead" is a very unspecific description of your problem. So unspecified that it's impossible to give you any advice.

Have you tested if the problem is caused by some plugin installed on your site? Try with all 3rd party plugins (including any 3rd party theme) disabled to find out if one of them is causing the problem. At least try to narrow down the possible reasons. Also check the error log on your server in case there's a log entry containing more info about what might be wrong.

1. Disable all non-bundled plugins and try again.
2. Upgrade to latest Elgg v2.3.9

Is it only happening for a specific reply or can't you delete any discussion reply? If it's a general problem, you might have to upgrade to the latest Elgg version (as in this case it was probably a bug that has been fixed in the meantime). If it's only happening for one reply it might be that the database entry of this reply is broken for some reason. In this case it might help to use the dbvalidator plugin from https://github.com/Elgg/dbvalidator (best might be to download https://github.com/Elgg/dbvalidator/archive/master.zip as it contains fixes not available in a release yet) to see if it shows some faulty db entries (first make only a validate run to see if there's anything the plugin would even be able to fix and only make a fix run if errors are found and then only after backuping the database).

Without knowing which version of Elgg you are using I assume that you use some Elgg 2.x or 3.x version. The core language files are in the vendor/elgg/elgg/languages/ subfolder within the install directory of your Elgg site.

But you shouldn't modify the core files directly. It would be just a hassle if you upgrade your site to re-do the changes all the time. You can override the language strings of Elgg core (or any plugin) by creating a plugin that contains a language file for the target language you want to modify a language string of. You would just have to copy the corresponding line from the original language file and insert it in the language file of your plugin and there you can modify the string (right of =>) then. For changing language strings of other plugins you just have to make sure that your plugin is ordered below the other plugins for the change to take effect.

As an example of how such a plugin would have to look like you can use the "Rename the Wire" plugin (https://elgg.org/plugins/1497293). Just drop the language strings you don't want to modify from its language file and add your own (from the Elgg core or other plugin language files) you want to change. You can also add language files for other languages you want to make changes.

I'll try it

Thanks a lot