Learning a new language is a gratifying enterprise. I'm not going to tell you that it is always easy, but if you go down this road you will not regret it. Motivation often depends on having a clear purpose. The reasons below may help you find the stimulation you need.
Moving to a new country.
Learning the local language will make your integration in the local community a whole lot easier. Maybe many people in your new country speak English. Don't let that become the excuse not to learn the local language. It will allow you to integrate and connect with the local community in a whole other way. You also demonstrate an involvement and dedication to your new country that will be noticed.
Relatives and friends.
If you are around people who has a different first language from you learning their language will open up a whole new level in your relationship. Learning a language is also learning how to think and feel in a whole different way. Your relationships will change for the better.
At work.
Being able to speak more languages will increase your chances of getting a transfer, finding a new job, getting a promotion or going on business trips. When you work with people who from a different culture speaking their language will grease the skids for partnership and socializing. Maybe you deal with children and older people in you job. Speaking their first language will make their (and your) day a whole lot better.
Travel.
Even if you can get by with English, speaking the local language will change your travel experiences dramatically. Imagine being able to ask locals for restaurant tips, travel away from the tourist crowds, getting to know the locals and being able to read signs. It will really add another dimension to your vacation
Study abroad.
Speaking the local tongue will serve you well, even if the courses are in English. Living in a foreign country is the best way to learn a new language well. Don't let the opportunity get away. If you spend some time in advance learning the language you can be a part of the social scene from day one.
Get in touch with your roots.
Your family might have spoken a particular language in the past. If you have children you can learn it together as a family project. Once you have some proficiency try contacting relatives in the "old country" and plan a vacation. You will be treated like kings and see parts of the culture that would be otherwise closed to you.
Food.
Let say you enjoy the food or wine of a particular region. Speaking the language will make you a priced guest at any restaurant. If you enjoy making the food yourself all the best cookbooks will be available to you.
Personal development.
Learning a language is a personal challenge. It will also show you that there are different ways to view the world. The structure of your language determines how you think. A second language will offer you a different way to think about the world. You will also view you own culture and language through a new lens.
Whatever reason resonates with you I hope you will take on the challenge of learning a new language. It will be rewarding in more ways than you can think of and open up a larger part of the wold for you. Good luck!