lint: port deref nullptr diagnostics

Signed-off-by: David Wood <[email protected]>

Author: davidtwco

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

@@ -393,3 +393,6 @@ lint-builtin-clashing-extern-same-name = `{$this_fi}` redeclared with a differen
 lint-builtin-clashing-extern-diff-name = `{$this_fi}` redeclares `{$orig}` with a different signature
     .previous-decl-label = `{$orig}` previously declared here
     .mismatch-label = this signature doesn't match the previous declaration
+
+lint-builtin-deref-nullptr = dereferencing a null pointer
+    .label = this code causes undefined behavior when executed

compiler/rustc_lint/src/builtin.rs

@@ -3068,8 +3068,8 @@ impl<'tcx> LateLintPass<'tcx> for DerefNullPtr {
         if let rustc_hir::ExprKind::Unary(rustc_hir::UnOp::Deref, expr_deref) = expr.kind {
             if is_null_ptr(cx, expr_deref) {
                 cx.struct_span_lint(DEREF_NULLPTR, expr.span, |lint| {
-                    let mut err = lint.build("dereferencing a null pointer");
-                    err.span_label(expr.span, "this code causes undefined behavior when executed");
+                    let mut err = lint.build(fluent::lint::builtin_deref_nullptr);
+                    err.span_label(expr.span, fluent::lint::label);
                     err.emit();
                 });
             }