[i18n] Font UI fallbacks: insert replacement characters with template for Weblate compatibility (#11614)

Added in <https://github.com/koreader/koreader/pull/8722> and unproblematic for the past two years, but Weblate has now decided to complain about it to the extent of disabling translations:

> Error message
String contains control character: 'If some book titles, dictionary entries and such are not displayed well but shown as \ufffe\ufffe or ��, it may be necessary to download the required fonts for those languages. They can then be enabled as additional UI fallback fonts.\nFonts for many languages can be downloaded at:\n\nhttps://fonts.google.com/noto\n\nOnly fonts named "Noto Sans xyz" or "Noto Sans xyz UI" (regular, not bold nor italic, not Serif) will be available in this menu. However, bold fonts will be used if their corresponding regular fonts exist.'

frontend/ui/elements/font_ui_fallbacks.lua

@@ -50,13 +50,13 @@ local genFallbackCandidates = function()
     end
 end
 
-local more_info_text = _([[
-If some book titles, dictionary entries and such are not displayed well but shown as ￾￾ or <EFBFBD><EFBFBD>, it may be necessary to download the required fonts for those languages. They can then be enabled as additional UI fallback fonts.
+local more_info_text = T(_([[
+If some book titles, dictionary entries and such are not displayed well but shown as %1 or %2, it may be necessary to download the required fonts for those languages. They can then be enabled as additional UI fallback fonts.
 Fonts for many languages can be downloaded at:
 
 https://fonts.google.com/noto
 
-Only fonts named "Noto Sans xyz" or "Noto Sans xyz UI" (regular, not bold nor italic, not Serif) will be available in this menu. However, bold fonts will be used if their corresponding regular fonts exist.]])
+Only fonts named "Noto Sans xyz" or "Noto Sans xyz UI" (regular, not bold nor italic, not Serif) will be available in this menu. However, bold fonts will be used if their corresponding regular fonts exist.]]), "￾￾", "<EFBFBD><EFBFBD>")
 
 local getSubMenuItems = function()
     genFallbackCandidates()