fix: i18n: Use 'en' as default language

[julianwachholz]

Using 'cimode' as default language code will return the translation keys verbatim without doing interpolation. This is unwanted unless working directly on localization.

Fixes #3240

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Bundle Stats — desktop-client

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Files count	Total bundle size	% Changed
9	4.92 MB → 4.92 MB (+67 B)	+0.00%

Changeset

File	Δ	Size
src/i18n.ts	📈 +67 B (+10.21%)	656 B → 723 B

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static/js/index.js	3.19 MB → 3.19 MB (+67 B)	+0.00%

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Asset	File Size	% Changed
static/js/indexeddb-main-thread-worker-e59fee74.js	13.5 kB	0%
static/js/resize-observer.js	18.37 kB	0%
static/js/usePreviewTransactions.js	790 B	0%
static/js/BackgroundImage.js	122.29 kB	0%
static/js/AppliedFilters.js	27.55 kB	0%
static/js/narrow.js	77.55 kB	0%
static/js/wide.js	246.2 kB	0%
static/js/ReportRouter.js	1.24 MB	0%

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Files count	Total bundle size	% Changed
1	1.14 MB	0%

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Asset	File Size	% Changed
kcab.worker.js	1.14 MB	0%

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