fix bidi isolation mark wrapping in locale.translation

address #4396 (comment)

Auditors: @aekeus

Test Plan:
1. go to ledger panel, save recovery keys
2. verify that opening the saved file in the browser does not show non-ascii characters

app/locale.js

@@ -230,13 +230,19 @@ var ctx = null
 var translations = {}
 var lang = 'en-US'
 
+// todo: FSI/PDI stripping can probably be replaced once
+// https://github.com/l20n/l20n.js/commit/2fea50bf43c43a8e930a519a37f0f64f3626e885
+// is released
+const FSI = '\u2068'
+const PDI = '\u2069'
+
 // Return a translate token from cache or a placeholder
 // indicating that no translation is available
 exports.translation = function (token, replacements = {}) {
   if (translations[token]) {
     let returnVal = translations[token]
     for (var key in replacements) {
-      returnVal = returnVal.replace(new RegExp('{{\\s*' + key + '\\s*}}'), replacements[key])
+      returnVal = returnVal.replace(new RegExp(FSI + '{{\\s*' + key + '\\s*}}' + PDI), replacements[key])
     }
     return returnVal
   } else {