chore: refactored the UI locale handling

lib/bds/desktop/ui_locale.ex

@@ -0,0 +1,65 @@
+defmodule BDS.Desktop.UILocale do
+  @moduledoc """
+  Per-render UI locale binding for the desktop LiveView shell.
+
+  The shell renders the UI in the user's selected language, which can differ
+  from the OS locale and from the project's `mainLanguage`. Phoenix HEEx
+  templates call `translated/1,2` helpers without an explicit locale, so we
+  bind the active locale once per `render/1` and the helpers read it back.
+
+  This module encapsulates that binding so call sites do not touch the raw
+  process dictionary directly. Use `with_locale/2` around any render or
+  component that needs a locale binding; use `current/0` to read it.
+
+  Direct use of `Process.put(:bds_ui_locale, _)` or
+  `Process.get(:bds_ui_locale)` is forbidden outside this module.
+  """
+
+  @key :bds_ui_locale
+
+  @typedoc "A normalized UI locale code such as `\"en\"` or `\"de\"`."
+  @type locale :: String.t() | nil
+
+  @doc """
+  Bind `locale` for any subsequent reads of `current/0` in this process.
+
+  Used at LiveView render boundaries. The binding persists past the call
+  (mirroring per-process locale state) so that lazily evaluated child
+  components see the active locale. Each render boundary overwrites it.
+  """
+  @spec put(locale()) :: :ok
+  def put(locale) do
+    Process.put(@key, locale)
+    :ok
+  end
+
+  @doc """
+  Set the UI locale for the duration of `fun`, then restore the prior value.
+
+  Safe under exceptions: the prior binding is restored in an `after` clause.
+  Use this for short-lived non-LiveView contexts (background tasks, scripts)
+  where eager evaluation guarantees the binding is consumed before `fun`
+  returns. Do not use around LiveView `render/1` because the returned
+  `Phoenix.LiveView.Rendered` struct evaluates its dynamic parts lazily.
+  """
+  @spec with_locale(locale(), (-> result)) :: result when result: var
+  def with_locale(locale, fun) when is_function(fun, 0) do
+    previous = Process.get(@key)
+    Process.put(@key, locale)
+
+    try do
+      fun.()
+    after
+      restore(previous)
+    end
+  end
+
+  @doc """
+  Read the active UI locale binding for this process, or `nil` when unset.
+  """
+  @spec current() :: locale()
+  def current, do: Process.get(@key)
+
+  defp restore(nil), do: Process.delete(@key)
+  defp restore(value), do: Process.put(@key, value)
+end