fixes #18858 [backport] (#18868)

* fixes #18858 [backport]

* ensure async tests work with --experimental:strictEffects [backport]

* ensure async tests work with --experimental:strictEffects [backport]

lib/pure/unicode.nim

@@ -705,8 +705,11 @@ proc capitalize*(s: string): string {.noSideEffect,
   fastRuneAt(s, i, rune, doInc = true)
   result = $toUpper(rune) & substr(s, i)
 
+when not defined(nimHasEffectsOf):
+  {.pragma: effectsOf.}
+
 proc translate*(s: string, replacements: proc(key: string): string): string {.
-  rtl, extern: "nuc$1".} =
+  rtl, extern: "nuc$1", effectsOf: replacements.} =
   ## Translates words in a string using the ``replacements`` proc to substitute
   ## words inside ``s`` with their replacements.
   ##