Apologies for the late reply. I've set the culture on a test page to cs-CZ and this is what I see rendered in the form, right before the MS AJAX scripts are included:
var
__cultureInfo =
'{"name":"cs-CZ","numberFormat":{"CurrencyDecimalDigits":2,"CurrencyDecimalSeparator":",","IsReadOnly":true,"CurrencyGroupSizes":[3],"NumberGroupSizes":[3],"PercentGroupSizes":[3],"CurrencyGroupSeparator":" ","CurrencySymbol":"Kč","NaNSymbol":"Není číslo","CurrencyNegativePattern":8,"NumberNegativePattern":1,"PercentPositivePattern":1,"PercentNegativePattern":1,"NegativeInfinitySymbol":"-nekonečno","NegativeSign":"-","NumberDecimalDigits":2,"NumberDecimalSeparator":",","NumberGroupSeparator":" ","CurrencyPositivePattern":3,"PositiveInfinitySymbol":"+nekonečno","PositiveSign":"+","PercentDecimalDigits":2,"PercentDecimalSeparator":",","PercentGroupSeparator":" ","PercentSymbol":"%","PerMilleSymbol":"‰","NativeDigits":["0","1","2","3","4","5","6","7","8","9"],"DigitSubstitution":1},"dateTimeFormat":{"AMDesignator":"dop.","Calendar":{"MinSupportedDateTime":"\/Date(-62135596800000)\/","MaxSupportedDateTime":"\/Date(253402293599999)\/","AlgorithmType":1,"CalendarType":1,"Eras":[1],"TwoDigitYearMax":2029,"IsReadOnly":true},"DateSeparator":".","FirstDayOfWeek":1,"CalendarWeekRule":0,"FullDateTimePattern":"d. MMMM yyyy H:mm:ss","LongDatePattern":"d. MMMM yyyy","LongTimePattern":"H:mm:ss","MonthDayPattern":"dd MMMM","PMDesignator":"odp.","RFC1123Pattern":"ddd, dd MMM yyyy HH\u0027:\u0027mm\u0027:\u0027ss \u0027GMT\u0027","ShortDatePattern":"d.M.yyyy","ShortTimePattern":"H:mm","SortableDateTimePattern":"yyyy\u0027-\u0027MM\u0027-\u0027dd\u0027T\u0027HH\u0027:\u0027mm\u0027:\u0027ss","TimeSeparator":":","UniversalSortableDateTimePattern":"yyyy\u0027-\u0027MM\u0027-\u0027dd HH\u0027:\u0027mm\u0027:\u0027ss\u0027Z\u0027","YearMonthPattern":"MMMM yyyy","AbbreviatedDayNames":["ne","po","út","st","čt","pá","so"],"ShortestDayNames":["ne","po","út","st","čt","pá","so"],"DayNames":["neděle","pondělí","úterý","středa","čtvrtek","pátek","sobota"],"AbbreviatedMonthNames":["I","II","III","IV","V","VI","VII","VIII","IX","X","XI","XII",""],"MonthNames":["leden","únor","březen","duben","květen","červen","červenec","srpen","září","říjen","listopad","prosinec",""],"IsReadOnly":true,"NativeCalendarName":"gregoriánský kalendář","AbbreviatedMonthGenitiveNames":["I","II","III","IV","V","VI","VII","VIII","IX","X","XI","XII",""],"MonthGenitiveNames":["ledna","února","března","dubna","května","června","července","srpna","září","října","listopadu","prosince",""]}}'
;
If this is on your page, your localization should be working. We'll be able to check this, as well for any other possible issues, if you can indeed grant us temporary access to the live application.
If all else fails and we can't persuade ASP.NET to render it you can just add this in a script tag right after the opening form tag.