feat(findbyid): Add lang query param for placeholder

This will reduce network transfer and speedup requests
Related: https://github.com/pelias/placeholder/pull/128

service/configurations/Language.js

@@ -15,12 +15,18 @@ class Language extends ServiceConfiguration {
       Array.prototype.push.apply(acc, _.values(_.pickBy(doc.parent, (v, k) => _.endsWith(k, '_id') ) ) );
       return acc;
     }, []);
-
+    const lang = _.get(req, 'clean.lang.iso6393');
-    return {
+    const parameters = {
       // arrays will be nested, so flatten first, then uniqify, and finally join elements with comma
       ids: _.uniq(_.flattenDeep(ids)).join(',')
     };
 
+    if (lang) {
+      parameters.lang = lang;
+    }
+
+    return parameters;
+
   }
 
   getUrl(req) {

test/unit/service/configurations/Language.js

@@ -117,6 +117,24 @@ module.exports.tests.all = (test, common) => {
 
   });
 
+
+  test('getParameters should return lang when req.clean.lang.iso6393 is defined', (t) => {
+    const configBlob = {
+      url: 'http://localhost:1234',
+      timeout: 17,
+      retries: 19
+    };
+
+    const req = {clean: {lang: {iso6393: 'eng' }}};
+    const res = { };
+
+    const language = new Language(configBlob);
+
+    t.deepEquals(language.getParameters(req, res), { ids: '', lang: 'eng' });
+    t.end();
+
+  });
+
   test('getHeaders should return empty object', (t) => {
     const configBlob = {
       url: 'base url',