If you are planning on a holiday to Laos, it is always a good idea to learn simple phrases like greetings before arriving. Not only will you find it easier to communicate, but many Lao people will appreciate the efforts you have made.
Of course you don't need to be fluent in speaking Lao language if you only plan to stay in Laos for a short time, because after you come home you will forget the language anyway unless you continue to speak Lao in your country. But a basic ability in Lao language will help you to get by in Laos, exampe if you want to order food and drink, find your way around, buy tickets, etc.
If you have a more advanced knowledge of Lao language, you can have real conversations and you will gain a deeper understanding of Lao culture and history with the people you meet in Laos, which can be very interesting and will add a new dimension to your holiday.
Lao is not a hard language to learn and you can easily pick up a few words and phrases in a short time. If you are lucky enough to know a person from Laos, or someone who speaks the language you can practice speaking with them. This will reinforce your learning and your friend can correct your pronunciation and offer advice.
English is not widely understood outside the main shopping and tourist areas, especially in the countryside so knowing Lao language is necessary. Lao people also understand Thai language so communicating with them in Thai is also acceptable.
Well that's it. Have fun learning Lao because it will completely transform your travel experience.
Sork dee! "Good luck!"