Extremely slow spreadsheet with certain Windows Regional Settings

Reporting very unusual problem with an Excel spreadsheet.
The spreadsheet loading time & flicking through values within the drop down menus varies considerably depending on the Windows Regional Settings.
I need to solve this ‘performance problem’ asap, but cannot find any logical explanation or any related issues online.

I have a few macros in a spreadsheet:
• Marco 1 run each time you open a workbook (to hide rows/columns etc…) it also calls Macro 2
• Macro 2 runs each time you flick through the drop down menu values to hide the unnecessary columns.

When I open the spreadsheet with English, Portuguese or Polish regional settings active, the spreadsheet performance is good (see table below).
However, if French, Czech Republic, Dutch or Croatian regional settings are active, the spreadsheet performance is very poor (see table below).
I have not tested all regional settings, but even with the these, it does not make any logical sense.

Below are timings:
Opening Flicking through drop down values
• Spreadsheet opening time: 1 min 8 sec (poor performance: French, Czech Rep, Dutch, Croatian)
• Flicking through drop downs: 44 sec (poor performance: French, Czech Rep, Dutch, Croatian)
• Spreadsheet opening time: 16 sec (good performance: English, Portuguese, Polish)
• Flicking through drop downs: 6 sec (good performance: English, Portuguese, Polish)

The issues does not seem to be related to decimal separators (comma vs dot), which vary from country to country.
I.e. Both French & Portuguese both use comma as a decimal separator, even though French setting is slow & Portuguese is fast.

I tried modified the spreadsheet settings in Options \ Advanced \ Editing Options \ Use system separators (in Excel 2010).
I.e. I unticked the box to ‘use system separators’ & tried putting various separators manually, but still the performance was poor/slow depending on the current regional settings…

Environments tested:
1. Windows 7, 4GB RAM Office 2007 32bit (1 machine tested)
2. Windows 7, 4GB RAM Office 2010 32bit (5 machine tested)
3. Windows 8, 8GB RAM Office 2013 64bit (1 machine tested)
I have not observed any differences in the behaviour between Office 2010 & 2013, however, in Office 2007 I experienced the overall slow performance, regardless of the Windows Regional Settings (possibly because of an older machine with slower processor/motherboard – cannot be 100% sure ).

About the ‘problematic’ spreadsheet:
• Size ~3MB
• 10 sheets (5 input + 5 output)
• The input sheets contain lot of data e.g. 3000-6000 rows by 30-50 columns.
• The output sheet leverage the following key Excel functions to manipulate/retrieve data: OFFSET, VLOOKUP, INDIRECT

I did another test, i.e. disabled the above macros from running, to see if that will have any impact on the timings.
Overall, the timings went down, but proportionally, i.e. still French, Czech etc... were much slower than English, Portuguese etc...


Any help will be much appreciated

Thank you.