Standardizing value format is a configuration that organizes your project fields better. Your different sources (online store, external system, external file) may provide different formats for the same value (language, country, gender, etc.). This can cause problems in certain situations, such as managing multilingual emails. For example, if you have different values for each contact who speaks English (see the image), the system might not recognize that some values correspond to English. Your contact may not receive a message targeted at contact with English as their language.
How To
Go to the edition of the field you want to standardize and click Configure:
Select existing values from the list and manually enter other values that might imported later. Then, indicate the value that you want to use as a standard ("EN" in this example):
Thus, imported values that are written as "English", "English (CA)", English (US)" and "Anglais" will be replaced by "EN" in the contact's profile which was imported or updated.
If you want to add other values to standardize, for example, for French, click Add standardization.
Results
When standardization is processed, it applies retroactively to already imported values. In the future, standardization will apply automatically to imports and updates. 
To make sure to see up-to-date values in the contact list, click the refresh button at the top of the list: