According to translate.google.com your error on the downloads translates to "While scanning this file with antivirus software there is an unexpected error." That kind of nonspecific error often indicates a conflict due to more than one active antivirus program, or a corrupt antivirus program. Did you recently update and/or run any anti-virus/anti-malware program (including Windows Defender) OR download another program on the advice of a popup from a website? If that last, you might have downloaded what is known as "scareware" at best, or something worse -- If that is the case, do NOT continue here but please go post in one of the infection topics.
Research indicates your download problem MAY be due to a corrupt Windows Defender. Does the computer with the problem have Windows Defender on it? Windows 7? Try Start > Control Panel (maybe "Configuratiescherm") and see if Windows Defender (maybe still "Windows Defender" or "Windows Verdediger") is on the list. If so, open it up and look at the History ("geschiedenis" or maybe "historie") link at that top where it will tell you if anything has been deleted or quarantined by that program. Try to restore whatever you find in there. Also in Windows Defender, next to the History link, you should find Tools (maybe "gereedschap") and in there Options ("opties"), and uncheck the box at the top that will disable auto daily scanning and then Save at the lower right. Then third on the menu on the left click on the Real-Time Protection link - also uncheck the top box and click on Save at the lower right.
Then back at the Tools link, the second link down on the left should be Quarantined Items ("quarantaine") - click on that and restore anything in there. Yes, I know I'm repeating, but if it's corrupt...
What other antivirus do you have? Look next to the clock and see if it's still there. If found, open it up and look in its quarantine and/or history. Use http://translate.google.com to help in identification if necessary. Some indications that AVG and/or Kaspersky might have had a conflict with Windows Defender in the past and won the fight, so it could happen with any of them.
Then try restarting the computer again and let us know if you're able to reset to English.