wallet: Avoid translating RPC errors when loading wallets

Common errors and warnings should be translated when displayed in the
GUI, but not translated when displayed elsewhere. The wallet method
CreateWalletFromFile does not know its caller, so this commit changes it
to return a bilingual_str to the caller.

src/qt/walletcontroller.h

@@ -8,6 +8,7 @@
 #include <qt/sendcoinsrecipient.h>
 #include <support/allocators/secure.h>
 #include <sync.h>
+#include <util/translation.h>
 
 #include <map>
 #include <memory>
@@ -104,8 +105,8 @@ protected:
     QWidget* const m_parent_widget;
     QProgressDialog* m_progress_dialog{nullptr};
     WalletModel* m_wallet_model{nullptr};
-    std::string m_error_message;
-    std::vector<std::string> m_warning_message;
+    bilingual_str m_error_message;
+    std::vector<bilingual_str> m_warning_message;
 };