Example to use grunt-wp-i18n makepot, update .po from .pot and grunt-po2mo

grunfile.js

module.exports = function(grunt) {

    grunt.initConfig({
        pkg: grunt.file.readJSON('package.json'),

        // LESS Compilation
        less: {
            development: {
                options: {
                    paths: ["src/css"]
                },
                files: {
                    'src/css/style.css': 'src/less/style.less',
                }
            },
        },

        // CSS minification
        cssmin: {
            combine: {
                options: {
                    // Remove comments
                    keepSpecialComments: 0
                },
                files: {
                    'assets/css/app.css': ['src/css/*.css']
                }
            }
        },

        // CSS autoprefixer
        autoprefixer: {
            single_file: {
                options: {
                // Target-specific options go here.
                },
                src: 'assets/css/app.css',
                dest: 'assets/css/app.css'
            },
        },

        // JS concatenation
        concat: {
            dist: {
                src: ['src/js/*.js'],
                dest: 'assets/js/app.js',
            },
        },

        // JS minification
        uglify: {
            dist: {
                files: {
                    'assets/js/app.min.js': ['assets/js/app.js']
                }
            }
        },

        // Watch css files
        watch: {
            less: {
                files: 'src/less/*.less',
                tasks: ['less'],
            },
            css: {
                files: ['src/css/*.css'],
                tasks: ['cssmin', 'autoprefixer'],
            },
            js: {
                files: 'src/js/*.js',
                tasks: ['concat', 'uglify'],
            },
        },


		// Generate POT file
		makepot: {
			target: {
				options: {
					mainFile: 'style.css',
					domainPath: '/languages',				// Where to save the POT file.
					type: 'wp-theme',						// Type of project (wp-plugin or wp-theme).
					potFilename: 'my-theme-name-v-1.pot',
					updateTimestamp: true,					// Whether the POT-Creation-Date should be updated without other changes.
					potHeaders: {							// Headers to add to the generated POT file.
						poedit: true,						// Includes common Poedit headers.
						'last-translator': 'Name Last <name@mail.com>',
						'language-team': 'Name Last <name@mail.com>',
						'plural-forms': 'nplurals=2; plural=(n != 1);',
						'language': 'en',
						'x-poedit-country': 'Spain',
						'x-poedit-language': 'Spanish',
						'x-poedit-sourcecharset': 'UTF-8',
						'x-poedit-basepath': '../',
						'x-poedit-searchpath-0': '.',
						'x-poedit-bookmarks': '',
						'x-textdomain-support': 'yes',
						'x-poedit-keywordslist': true		// Include a list of all possible gettext functions.
					},                                
					updatePoFiles: true,					//To use this option is need to have gettext installed.
															//For OSX install http://brew.sh
															//Open Terminal and paste: `brew install gettext`
															//And link it: `brew link gettext --force`
															//The reason you need to link gettext is because OSX already ships with 
															//gettext and brew is conservative about it.
				}
			}
		},
		
		// Generate .mo from .po
		po2mo: {
		files: {
		src: 'languages/es_ES.po',
		dest: 'languages/es_ES.mo',
		},
		files: {
		src: 'languages/ca.po',
		dest: 'languages/ca.mo',
		},
		files: {
		src: 'languages/de_DE.po',
		dest: 'languages/de_DE.mo',
		},
		},
        
    });

    // Load Grunt plugins
    require('load-grunt-tasks')(grunt);

    // Set up Grunt tasks
    grunt.registerTask('css', ['less', 'cssmin', 'autoprefixer']);
    grunt.registerTask('js', ['concat', 'uglify']);
    grunt.registerTask('translate', ['makepot', 'po2mo']);    
    grunt.registerTask('default', ['css', 'js', 'makepot']);
};