diff --git a/src/metabase/server/routes/index.clj b/src/metabase/server/routes/index.clj
index 11119f3f193fb540958edcd868d7d59fd459bae5..5ca6bdd0befe4e05473e679173e7a89e0a3fb60c 100644
--- a/src/metabase/server/routes/index.clj
+++ b/src/metabase/server/routes/index.clj
@@ -35,26 +35,26 @@
     {"" {"Metabase" {"msgid"  "Metabase"
                      "msgstr" ["Metabase"]}}}}))
 
-(defn- localization-json-file-name [locale-or-name]
-  (format "frontend_client/app/locales/%s.json" (str (i18n/locale locale-or-name))))
+(defn- localization-json-file-name [locale-string]
+  (format "frontend_client/app/locales/%s.json" (str/replace locale-string \- \_)))
 
-(defn- load-localization* [locale-or-name]
+(defn- load-localization* [locale-string]
   (or
-   (when-let [locale-name (some-> locale-or-name str)]
-     (when-not (= locale-name "en")
+   (when locale-string
+     (when-not (= locale-string "en")
        (try
-         (slurp (or (io/resource (localization-json-file-name locale-name))
-                    (when-let [fallback-locale (i18n/fallback-locale locale-name)]
+         (slurp (or (io/resource (localization-json-file-name locale-string))
+                    (when-let [fallback-locale (i18n/fallback-locale locale-string)]
                       (io/resource (localization-json-file-name (str fallback-locale))))
                     ;; don't try to i18n the Exception message below, we have no locale to translate it to!
-                    (throw (FileNotFoundException. (format "Locale '%s' not found." locale-name)))))
+                    (throw (FileNotFoundException. (format "Locale '%s' not found." locale-string)))))
          (catch Throwable e
            (log/warn (.getMessage e))))))
-   (fallback-localization locale-or-name)))
+   (fallback-localization locale-string)))
 
 (def ^:private ^{:arglists '([])} load-localization
   "Load a JSON-encoded map of localized strings for the current user's Locale."
-  (comp (memoize load-localization*) #(some-> (i18n/user-locale) str)))
+  (comp (memoize load-localization*) #(i18n/user-locale-string)))
 
 (defn- load-inline-js* [resource-name]
   (slurp (io/resource (format "frontend_client/inline_js/%s.js" resource-name))))
diff --git a/src/metabase/util/i18n.clj b/src/metabase/util/i18n.clj
index 60d767c64233601411ba83f3f266eeadeeb6fb5a..3b04846ed5e614e3ca56808da8e6c8335547f3ed 100644
--- a/src/metabase/util/i18n.clj
+++ b/src/metabase/util/i18n.clj
@@ -25,25 +25,35 @@
   nil)
 
 (def ^:dynamic *site-locale-override*
-  "Bind this to a string, keyword, or `Locale` to override the value returned by `site-locale`. For testing purposes,
+  "Bind this to a string, keyword to override the value returned by `site-locale`. For testing purposes,
   such as when swapping out an application database temporarily, when the setting table may not even exist."
   nil)
 
+(defn site-locale-string
+  "The default locale string for this Metabase installation. Normally this is the value of the `site-locale` Setting,
+  which is also a string."
+  []
+  (or *site-locale-override*
+      (i18n.impl/site-locale-from-setting)
+      "en"))
+
+(defn user-locale-string
+  "Locale string we should *use* for the current User (e.g. `tru` messages) -- `*user-locale*` if bound, otherwise the
+  system locale as a string."
+  []
+  (or *user-locale*
+      (site-locale-string)))
+
 (defn site-locale
   "The default locale for this Metabase installation. Normally this is the value of the `site-locale` Setting."
   ^Locale []
-  (locale (or *site-locale-override*
-              (i18n.impl/site-locale-from-setting)
-              ;; if DB is not initialized yet fall back to English
-              "en")))
+  (locale (site-locale-string)))
 
 (defn user-locale
   "Locale we should *use* for the current User (e.g. `tru` messages) -- `*user-locale*` if bound, otherwise the system
   locale."
   ^Locale []
-  (locale
-   (or *user-locale*
-       (site-locale))))
+  (locale (user-locale-string)))
 
 (defn available-locales-with-names
   "Returns all locale abbreviations and their full names"
@@ -57,7 +67,8 @@
   "Translate a string with the System locale."
   [format-string & args]
   (let [translated (apply translate (site-locale) format-string args)]
-    (log/tracef "Translated %s for site locale %s -> %s" (pr-str format-string) (pr-str (site-locale)) (pr-str translated))
+    (log/tracef "Translated %s for site locale %s -> %s"
+                (pr-str format-string) (pr-str (site-locale-string)) (pr-str translated))
     translated))
 
 (defn translate-user-locale
@@ -65,7 +76,8 @@
   [format-string & args]
   (let [translated (apply translate (user-locale) format-string args)]
     (log/tracef "Translating %s for user locale %s (site locale %s) -> %s"
-                (pr-str format-string) (pr-str (user-locale)) (pr-str (site-locale)) (pr-str translated))
+                (pr-str format-string) (pr-str (user-locale-string))
+                (pr-str (site-locale-string)) (pr-str translated))
     translated))
 
 (p.types/defrecord+ UserLocalizedString [format-string args]