fix(util/i18n): Memoize language options

lib/util/i18n.js

@@ -1,5 +1,6 @@
 import clone from 'clone'
 import flatten from 'flat'
+import memoize from 'lodash.memoize'
 
 // deepmerge must be imported via `require`: see https://github.com/TehShrike/deepmerge#include
 const merge = require('deepmerge')
@@ -63,7 +64,7 @@ export function getConfigLocales(configLanguages) {
  * @param {*} configLanguages The configured languages.
  * @returns An array of the supported locale ids if 2 or more are configured, null otherwise.
  */
-export function getLanguageOptions(configLanguages) {
+export const getLanguageOptions = memoize((configLanguages) => {
   const filteredKeys =
     (configLanguages &&
       Object.keys(configLanguages).filter(
@@ -77,7 +78,7 @@ export function getLanguageOptions(configLanguages) {
     filteredLanguages[key] = configLanguages[key]
   })
   return filteredLanguages
-}
+})
 
 /**
  * Loads in all localized strings from @opentripplanner packages.