Add Localization section to Swift Style Guide (#590)

* Add crowdin section

* Un-wishy-wash

* Add link to company Crowdin documentation

Author: KatherineInCode

docs/contributing/code-style/swift.md

@@ -1,7 +1,3 @@
----
-title: Swift
----
-
 # Swift
 
 We use both [SwiftLint](https://github.com/realm/SwiftLint) and
@@ -146,6 +142,33 @@ class ClassName {
 - We prefer "Tapped" instead of "Pressed", "Touched", or "Clicked" when describing buttons or other
   screen elements being tapped, in line with Apple calling this a tap gesture.
 
+## Localization
+
+- We use Crowdin to crowd-source our localizations, based off of the English text. More information
+  on how to contribute translations and how we use Crowdin within Bitwarden can be found
+  [here](https://contributing.bitwarden.com/contributing/#localization-l10n).
+- We use `.strings` files for localization. Therefore only the English `Localizable.strings` file
+  needs to be updated when adding strings; we have regular jobs in GitHub that take care of syncing
+  other translations with Crowdin.
+- Keys in `Localizable.strings` should be a CamelCased string of the English text, rather than a
+  description of where the key is used. As a result, if the English text changes, the key should
+  likewise change—this allows translators in Crowdin to know that they need to likewise update the
+  localized text.
+- Contractions can be converted to un-contracted form in the key, particularly if it aids with
+  readability.
+- If the string in question is particularly long, a truncated form with `DescriptionLong` appended
+  is reasonable.
+- If possible, keys (and therefore corresponding localized text) should be the same between iOS and
+  Android.
+
+Some examples:
+
+```text
+"UseFingerprintToUnlock" = "Use fingerprint to unlock";
+"EncryptionKeyMigrationRequiredDescriptionLong" = "Encryption key migration required. Please login through the web vault to update your encryption key.";
+"YouAreAllSet" = "You're all set!";
+```
+
 ## File Names
 
 - Swift files are named per Swift convention of CamelCase of the primary class name in the file.