* Unang Digmaang Pandaigdig (Literally: First World War)
* Digmaang Pandaigdig I (Literally: World War I)
These translations are commonly used in the Philippines and are easily understood by Tagalog speakers.
You can also use other phrases depending on the context, such as:
* Digmaan noong 1914-1918 (The War of 1914-1918)
* Dakilang Digmaan (Great War) - This is an older term, sometimes used as a synonym for World War 1
Remember that the term "World War" is a modern concept, so translating it into Tagalog might not have a precise equivalent.