utc_to_local(DateTime, Timezone) - converts UTC time to local according to specified Timezone
local_to_utc(DateTime, Timezone) - converts local time to UTC
local_to_local(DateTime, TimezoneFrom, TimezoneTo) - converts local time to local
tz_name(DateTime, Timezone) - returns a timezone name (E.g. MSK, MSD, etc)
tz_shift(DateTime, Timezone) - returns time difference between local datetime and GMT
tz_shift(DateTime, TimezoneFrom, TimezoneTo) - returns time difference between local datetime and required timezone Where DateTime = {date(), time()} TimeZone(To, From) = String(). E.g. “Europe/Moscow”, “America/NewYork”. Or abbreviations "MSK", "MSD", etc. Note: abbreviation is just used to find appropriate timezone name. If you want to convert "MSK" -> "PDT", but source timezone is not in daylight saving, it will be corrected by library and "MSK" -> "PST" conversion will be made.

Converts UTC time to local one

localtime:utc_to_local({{2010, 7, 22}, {17, 56, 23}, "Europe/Moscow").
{{2010,10,10},{21,56,23}}

Converts local time to UTC one

localtime:local_to_utc({{2010, 10, 10}, {21, 56, 23}}, "Europe/Moscow").
{{2010,10,10},{17,56,23}}

Converts time from one local timezone to another local one

localtime:local_to_local({{2010, 10, 10}, {21, 56, 23}}, "Europe/Moscow", "Australia/Sydney").
{{2010,10,11},{3,56,23}}

Returns timezone name

localtime:tz_name({{2010, 10, 10}, {21, 56, 23}}, "Europe/Moscow").
{"MSK","MSK"}

localtime:tz_name({{2010,10,11},{3,56,23}}, "Australia/Sydney").
{"EST","EST"}

Calculates time difference between UTC and local one

localtime:tz_shift({{2013, 01, 22}, {18, 17, 00}}, "Europe/Moscow").
{'+',4,0}

localtime:tz_shift({{2013, 01, 22}, {18, 17, 00}}, "America/New York").
{'-',5,0}

Calculates time difference between two local timezones

localtime:tz_shift({{2013, 01, 22}, {18, 17, 00}}, "America/New York", "Europe/Moscow").
{'+',9,0}