The language code for the PayPal site is defined in the button using a hidden field.
So for English language use
<input type=’hidden’ name=’lc’ value=’US’ />
Possible values are France(FR), Spain (ES), Italy (IT), Germany (DE), China (CN), English (US).
The customer should hopefully see the login page in the defined language.
To change the language code, go to the file ipnfunction.php open in a text editor and you should see the default language code of
<input type=’hidden’ name=’lc’ value=’US’ />
Change the value to what ever code you require and upload the file back to your server.