Added note about "Inconsistent types declared for an argument: U_ARGUMENT_TYPE_MISMATCH" ICU error to i18n docs

docs/guide/i18n.md

@@ -232,6 +232,13 @@ for Russian:
 
 In the above it worth mentioning that `=1` matches exactly `n = 1` while `one` matches `21` or `101`.
 
+Note that if you are using placeholder twice and one time it's used as plural another one should be used as number else
+you'll get "Inconsistent types declared for an argument: U_ARGUMENT_TYPE_MISMATCH" error:
+
+```
+Total {count, number} {count, plural, one{item} other{items}}.
+```
+
 To learn which inflection forms you should specify for your language you can referer to
 [rules reference at unicode.org](http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html).