The following are common factors to consider:

• language
• unit of measure (e.g., kilometers in Europe, miles in U.S.)
• text direction (e.g., European languages are left-to-right, Arabic right-to-left)
• capitalization in Latin script (e.g., English uses capitals for weekdays, Spanish uses lowercase)
• adaptation of idioms (e.g., "raining cats and dogs" makes no sense when translated literally)
• use of register (e.g., in Japanese respectful speech differs exceptionally from casual speech)
• number format (e.g., 10 000,00 in Germany vs. 10,000.00 in the U.S.)
• date format
• currency
• cultural references
• paper size
• color psychology
• compliance with local laws
• local holidays
• personal names

The complementary practice, of designing a system so it is easy to localize, is called Internationalization .