如何使用毒蛇将环境变量解组到切片？

I have the following code:

package main

import (
    "log"

    "github.com/spf13/viper"
)

func main() {
    viper.SetEnvPrefix("myprefix")
    viper.SetDefault("languages", []string{"french", "spanish"})
    viper.BindEnv("name")
    viper.BindEnv("languages")

    type config struct {
        Name      string
        Languages []string
    }

    var C config

    err := viper.Unmarshal(&C)
    if err != nil {
        log.Fatalln("unable to decode into struct, %v", err)
    }

    log.Println(C)
    log.Println(len(C.Languages))
}

When $MYPREFIX_LANGUAGES is not set the length of C.Languages is 2 (eg the default). When I set $MYPREFIX_LANGUAGES to "english spanish french russian" I get a length of 1. It is just taking the variable as 1 long string, not a slice. How do I get a slice ([]string{"english", "spanish", "french", "russian"}?

Thanks to @Charlino here is the answer:

package main

import (
    "log"

    "github.com/spf13/viper"
)

func main() {
    viper.SetEnvPrefix("myprefix")
    viper.SetTypeByDefaultValue(true)
    viper.SetDefault("languages", []string{"french", "spanish"})
    viper.BindEnv("name")
    viper.BindEnv("languages")

    type config struct {
        Name      string
        Languages []string
    }

    var C config

    err := viper.Unmarshal(&C)
    if err != nil {
        log.Fatalln("unable to decode into struct, %v", err)
    }

    log.Println(C)
    log.Println(len(C.Languages))
}