Detect default locale with fallback IETF BCP 47 language tag

[shaedrich]

Describe the bug
When using IETF BCP 47 language tags instead of just ISO 639-1 language codes, the default language code translation file should be determined from the IETF BCP 47 language tag

Might be related to #1172 and/or #787

Extension Version
i18n Ally (v2.13.1)

Framework/i18n package you are using
vue-i18n

To Reproduce
Steps to reproduce the behavior:

1. Have a file called en-GB.json instead of en.json
2. Go to any file using translations
3. Hover over the translation function
4. See error

Device Infomation

• OS: Ubuntu/Linux x64
• Version: 24.04.1 LTS
• VS Code Version: 1.96.2 (fabdb6a30b49f79a7aba0f2ad9df9b399473380f, 2024-12-19T10:22:47.216Z)

Extension Log
Go to View -> Output -> i18n Ally, and paste the content below. You should mask (***) any sensitive information

🈶 Activated, v2.13.1

――――――

💼 Workspace root changed to "***"
📦 Packages file "package.json" found
🕳 Packages file "pubspec.yaml" not exists
🕳 Packages file "composer.json" not exists
🕳 Packages file "Gemfile" not exists
🧰 Config "i18n-ally.localesPaths" changed, reloading
🔁 Reloading loader
📦 Packages file "package.json" found
🕳 Packages file "pubspec.yaml" not exists
🕳 Packages file "composer.json" not exists
🕳 Packages file "Gemfile" not exists
🌞 Enabled
🧩 Enabled frameworks: Vue, General, Vue SFC
🧬 Enabled parsers: json, yaml, json5

📈 Telemetry id: 2e41e13e-6de9-423c-bd3c-f483145704a4
🚀 Initializing loader "***"
📂 Directory structure: file
🗃 Path Matcher Regex: /^(?<locale>[\w-_]+)\.(?<ext>json|ya?ml|json5)$/

📂 Loading locales under ***/src/locales
	📑 Loading (de-DE) de-DE.json [1736334472496.4211]
	📑 Loading (en-GB) en-GB.json [1736334472497.4211]

👀 Watching change on ***/src/locales
✅ Loading finished


――――――

🧰 Config "i18n-ally.localesPaths" changed, reloading
🔁 Reloading loader
📦 Packages file "package.json" found
🕳 Packages file "pubspec.yaml" not exists
🕳 Packages file "composer.json" not exists
🕳 Packages file "Gemfile" not exists
🧩 Enabled frameworks: Vue, General, Vue SFC
🧬 Enabled parsers: json, yaml, json5

🚀 Initializing loader "***"
📂 Directory structure: file
🗃 Path Matcher Regex: /^(?<locale>[\w-_]+)\.(?<ext>json|ya?ml|json5)$/

📂 Loading locales under ***/src/locales
	📑 Loading (de-DE) de-DE.json [1736334472496.4211]
	📑 Loading (en-GB) en-GB.json [1736334472497.4211]

👀 Watching change on ***/src/locales
✅ Loading finished


――――――

📑 Loading sfc ***/src/components/***.vue
📑 Loading sfc ***/src/components/***.vue
📑 Loading sfc ***/src/components/***.vue
📑 Loading sfc ***/src/components/***.vue

Screenshots