lint: port translation migration diagnostics

Signed-off-by: David Wood <david.wood@huawei.com>

Author: davidtwco

compiler/rustc_error_messages/locales/en-US/lint.ftl

@@ -49,3 +49,8 @@ lint-lintpass-by-hand = implementing `LintPass` by hand
 
 lint-non-existant-doc-keyword = found non-existing keyword `{$keyword}` used in `#[doc(keyword = \"...\")]`
     .help = only existing keywords are allowed in core/std
+
+lint-diag-out-of-impl =
+    diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls
+
+lint-untranslatable-diag = diagnostics should be created using translatable messages

compiler/rustc_lint/src/internal.rs

@@ -423,8 +423,7 @@ impl LateLintPass<'_> for Diagnostics {
         debug!(?found_impl);
         if !found_impl {
             cx.struct_span_lint(DIAGNOSTIC_OUTSIDE_OF_IMPL, span, |lint| {
-                lint.build("diagnostics should only be created in `SessionDiagnostic`/`AddSubdiagnostic` impls")
-                    .emit();
+                lint.build(fluent::lint::diag_out_of_impl).emit();
             })
         }
 
@@ -442,7 +441,7 @@ impl LateLintPass<'_> for Diagnostics {
         debug!(?found_diagnostic_message);
         if !found_diagnostic_message {
             cx.struct_span_lint(UNTRANSLATABLE_DIAGNOSTIC, span, |lint| {
-                lint.build("diagnostics should be created using translatable messages").emit();
+                lint.build(fluent::lint::untranslatable_diag).emit();
             })
         }
     }