hello: fix translations on FreeBSD

pkgs/by-name/he/hello/package.nix

@@ -7,6 +7,7 @@
   testers,
   versionCheckHook,
   hello,
+  gettext,
   gnulib,
 }:
 
@@ -30,6 +31,10 @@ stdenv.mkDerivation (finalAttrs: {
     NIX_LDFLAGS = "-liconv";
   };
 
+  buildInputs = lib.optionals stdenv.hostPlatform.isFreeBSD [
+    gettext
+  ];
+
   doCheck = true;
 
   doInstallCheck = true;