The flag module can be used with the i18n package. It requires some extra configuration of the default module settings, but eventually you can get to a point where:

1. Flagging a node actually flags the original source node (essentially flagging all the node's translations).
2. Loading the "My bookmarks" page will show the current language flagged nodes' translations.

Here are the steps:

1. Install the Translation helpers module.
2. Go to the Flags admin page and add/edit a flag (for this manual we'll use the default bookmarks flag).
3. Under "Internationalization", check the "Flag translations of content as a group" option (this option become available with the Translation helpers module) and save the flag. Now, when a user flags a node, the source node will be flagged and all of the node's translations will appear flagged as well.
4. Now edit the "My bookmarks" View.
5. In "Relationships" add the "Node translation: Translations" relationship, and in its configuration set the "Translation option" to "Current language".
6. Edit each field you're displaying in "Fields" and set its Relationship to "Translations".
7. Save the View.

That's it! Now when the user browses to his "My bookmarks" page in language X, only flagged nodes with the X translation will appear and in the right language.