diff --git a/CHANGES b/CHANGES
index 5fab4671a36..bc932a7d48c 100644
--- a/CHANGES
+++ b/CHANGES
@@ -26,6 +26,7 @@ Features added
 * #7745: html: inventory is broken if the docname contains a space
 * #7902: html theme: Add a new option :confval:`globaltoc_maxdepth` to control
   the behavior of globaltoc in sidebar
+* #7840: i18n: Optimize the dependencies check on bootstrap
 * #7052: add ``:noindexentry:`` to the Python, C, C++, and Javascript domains.
   Update the documentation to better reflect the relationship between this option
   and the ``:noindex:`` option.
diff --git a/sphinx/environment/__init__.py b/sphinx/environment/__init__.py
index 1e58542bba2..cf3364494b7 100644
--- a/sphinx/environment/__init__.py
+++ b/sphinx/environment/__init__.py
@@ -387,11 +387,11 @@ def find_files(self, config: Config, builder: "Builder") -> None:
                 # add catalog mo file dependency
                 repo = CatalogRepository(self.srcdir, self.config.locale_dirs,
                                          self.config.language, self.config.source_encoding)
+                mo_paths = {c.domain: c.mo_path for c in repo.catalogs}
                 for docname in self.found_docs:
                     domain = docname_to_domain(docname, self.config.gettext_compact)
-                    for catalog in repo.catalogs:
-                        if catalog.domain == domain:
-                            self.dependencies[docname].add(catalog.mo_path)
+                    if domain in mo_paths:
+                        self.dependencies[docname].add(mo_paths[domain])
         except OSError as exc:
             raise DocumentError(__('Failed to scan documents in %s: %r') %
                                 (self.srcdir, exc)) from exc