The modern Mother’s Day is celebrated on various days in many parts of the world,
most commonly in May or in March/April, as a day to honour mothers and motherhood.
In the UK and Ireland it follows the old traditions of Mothering Sunday, celebrated in March/April.

More info at Wikipedia.

9 Feb
Norway

3 Mar
Georgia

8 Mar (International Women’s Day)
Afghanistan, Albania, Armenia, Azerbaijan, Belarus, Bosnia and Herzegovina, Bulgaria, Burkina Faso, Kazakhstan, Kosovo, Laos, Macedonia, Moldova, Montenegro, Romania, Russia, Serbia, Slovenia, Tajikistan, Uzbekistan, Vietnam

21 Mar (Spring Equinox)
Bahrain, Comoros, Djibouti, Egypt, Iraq, Jordan, Kuwait, Libya, Lebanon, Mauritania, Oman, Palestine, Qatar, Saudi Arabia, Somalia, Sudan, Syria, UnitedArabEmirates, Yemen

22 Mar (4th Sunday of Lent)
Guernsey, Ireland, Isle of Man, Jersey, Nigeria, United Kingdom

25 Mar
Slovenia

7 Apr (Annunciation Day)
Armenia

3 May
Angola, Cape Verde, Hungary, Lithuania, Mozambique, Portugal, Spain

8 May (Parent’s Day)
South Korea

10 May
El Salvador, Guatemala, Mexico

10 May
Anguilla, Antigua and Barbuda, Aruba, Australia, Austria, Bahamas, Bangladesh, Barbados, Belgium, Belize, Bermuda, Bhutan, Bonaire, Botswana, Brazil, Brunei, Canada, Cambodia, Cayman Islands, Central African Republic, Chad, Chile, China, Colombia, Congo, Dem. Rep., Congo, Rep., Cote d’Ivoire, Croatia, Cuba, Curaçao, Cyprus, Czech Republic, Denmark, Dominica, Ecuador, Equatorial Guinea, Estonia, Ethiopia, Faroe Islands, Fiji, Finland, Germany, Gabon, Gambia, Greenland, Ghana, Greece, Grenada, Guyana, Honduras, Hong Kong, Iceland, India, Italy, Jamaica, Japan, Kenya, Latvia, Liberia, Liechtenstein, Macau, Malaysia, Malta, Myanmar, Namibia, Netherlands, New Zealand, Pakistan, Papua New Guinea, Peru, Philippines, Puerto Rico, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Samoa, Singapore, Sint Maarten, Slovakia, South Africa, Sri Lanka, Suriname, Switzerland, Taiwan, Tanzania, Tonga, Trinidad and Tobago, Turkey, Uganda, Ukraine, United States, Uruguay, Vietnam, Venezuela, Zambia, Zimbabwe

14 May
Benin

15 May
Paraguay

19 May
Kyrgyzstan

22 May
Israel

26 May
Poland

27 May
Bolivia

30 May
Nicaragua

31 May
Algeria, Cameroon, Dominican Republic, Madagascar, Mali, Morocco, Niger, Haiti, Mauritius, Senegal, Sweden, Tunisia

1 Jun
Mongolia (Together with Children’s Day)

7 Jun
France, French Antilles

14 Jun
Luxembourg

6 Jul
South Sudan

12 Aug
Thailand

15 Aug
Costa Rica, Antwerp

14 Oct
Belarus

15 Oct
Malawi

18 Oct
Argentina

3 Nov
Timor Leste

16 Nov
North Korea

29 Nov
Russia

8 Dec
Panama

22 Dec
Indonesia