_Configuration:_
- Web browser and its version: 
   - **Edge**: 91.0.864.64 
   - **Chrome**: 91.0.4472.124
- PDF.js version:
   - Latest demo version: https://mozilla.github.io/pdf.js/web/viewer.html

_Steps to reproduce the problem:_
1. Open the demo viewer in Chrome
2. Open the demo viewer in Edge

_What is the expected behavior?_ 

The viewer should be localized, i.e. translated to Swedish.

_What went wrong? (add screenshot)_

The viewer is translated to Swedish in Chrome, but not in Edge.

_Request headers:_
  - Chrome: `Accept-Language: sv-SE,sv;q=0.9,en-US;q=0.8,en;q=0.7`
  - Edge: `Accept-Language: sv,en;q=0.9,en-GB;q=0.8,en-US;q=0.7`

The problem seems to be that the `l10n` folder does not contain an `sv` folder, but only an `sv-SE`. 
/* Copyright 2017 Mozilla Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
import "../external/webL10n/l10n.js";
import { getL10nFallback } from "./l10n_utils.js";
const webL10n = document.webL10n;
class GenericL10n {