(core) i18

Summary:
Adding initial work for localization support.

Summary in https://grist.quip.com/OtZKA6RHdQ6T/Internationalization-and-Localization

Test Plan: Not yet

Reviewers: paulfitz

Reviewed By: paulfitz

Subscribers: paulfitz

Differential Revision: https://phab.getgrist.com/D3633

package.json

@@ -41,6 +41,7 @@
     "@types/express": "4.16.0",
     "@types/form-data": "2.2.1",
     "@types/fs-extra": "5.0.4",
+    "@types/i18next-fs-backend": "1.1.2",
     "@types/image-size": "0.0.29",
     "@types/js-yaml": "3.11.2",
     "@types/jsdom": "16.2.14",
@@ -126,6 +127,9 @@
     "http-proxy-agent": "5.0.0",
     "https-proxy-agent": "5.0.1",
     "i18n-iso-countries": "6.1.0",
+    "i18next": "21.9.1",
+    "i18next-fs-backend": "1.1.5",
+    "i18next-http-middleware": "3.2.1",
     "image-size": "0.6.3",
     "jquery": "3.5.0",
     "js-yaml": "3.14.1",