Mass update user email encoding for email templates

To mass update the email encoding for all users in your Salesforce org, use the Data Loader to export, modify, and re-import the EmailEncodingKey field on User records. The EmailEncodingKey field determines the default character encoding used when a user creates an email template.

To update a User record's email encoding

1) Export the Users' Id and existing email template encoding.

a) Log in to the Data Loader.
b) Click Export.
c) Select the User (User) object.
d) Select ID, EmailEncodingKey, and any other fields that will be help validate the users being updated.  
e) Click Finish.

2) Update the exported user's EmailEncodingKey values in your resulting export's file.

Valid values include:

• UTF-8: “Unicode (UTF-8)” in the UI
• ISO-8859-1: “General US & Western Europe (ISO-8859–1, ISO-LATIN-1)” in the UI
• Shift_JIS: “Japanese (Shift-JIS)” in the UI
• ISO-2022-JP: “Japanese (JIS)” in the UI
• EUC-JP: “Japanese (EUC)” in the UI
• ks_c_5601-1987: “Korean (ks_c_5601–1987)” in the UI
• Big5: “Traditional Chinese (Big5)” in the UI
• GB2312: “Simplified Chinese (GB2312)” in the UI
• BIG5-HKSCS: “Traditional Chinese Hong Kong (Big5–HKSCS)” in the UI
• x-SJIS_0213: “Japanese (Shift-JIS_2004)” in the UI

3) Update the user records with the Data Loader.

a) Log in to the Data Loader.
b) Click Update.
c) Select the User (User) object. 
d) Select Browse and find your updated csv. file, click Next >.
e) Click Create or Edit a Map.
f) Map the fields.
g) Click Next and then Finish.

When users create an email template, the email encoding you have set in your update file will be selected by default.