I think I have solved problem.
Ads.english-utf8.php ( as well as Ads.english.php )
is included into PAY-ME mod
<<
http://www.smfads.com/forums/index.php?topic=1639.msg6628#msg6628 .
It is enough to display Ads Management option in Configuration
for Default SMF Core Theme
on UTF8 forum (and the operability of the mod on not utf8 forum does not suffer).
But it does not guarantee the display of the ads
for other custom themes which use their own *.template.php files.